experimental: renderer

.busted

@@ -1,12 +0,0 @@
-return {
-  _all = {
-    lpath = "lua/?.lua;lua/?/init.lua",
-    lua = "nvim -u NONE -i NONE -l",
-  },
-  default = {
-    verbose = true
-  },
-  tests = {
-    verbose = true
-  },
-}

.emmyrc.json

@@ -1,22 +0,0 @@
-{
-  "$schema": "https://raw.githubusercontent.com/EmmyLuaLs/emmylua-analyzer-rust/refs/heads/main/crates/emmylua_code_analysis/resources/schema.json",
-  "diagnostics": {
-    "disable": [
-      "access-invisible",
-      "redefined-local"
-    ]
-  },
-  "runtime": {
-    "version": "LuaJIT"
-  },
-  "workspace": {
-    "ignoreDir": [
-      ".prefix"
-    ],
-    "library": [
-      "$VIMRUNTIME",
-      "library/busted",
-      "library/luv"
-    ]
-  }
-}

.github/workflows/ci.yaml

@@ -1,60 +1,15 @@
 # yaml-language-server: $schema=https://json.schemastore.org/github-workflow.json
-name: ci
+name: NeoVim tests
-
+on: [push]
-on:
-  workflow_dispatch:
-  pull_request:
-  push:
-    tags: ["*"]
-    branches: ["*"]
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
-
-env:
-  MISE_EXPERIMENTAL: true
-
 jobs:
-  ci:
+  plenary-tests:
     runs-on: ubuntu-latest
-    timeout-minutes: 10
+    env:
+      XDG_CONFIG_HOME: ${{ github.workspace }}/.config/
     steps:
       - uses: actions/checkout@v4
+      - uses: rhysd/action-setup-vim@v1
         with:
-          submodules: true
+          neovim: true
-
+          version: v0.10.1
-      - name: Install apt dependencies
+      - run: make test
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y libreadline-dev
-
-      - name: Setup environment
-        run: |
-          if [ -n "${{secrets.TOKEN}}" ]; then
-            export GITHUB_TOKEN="${{secrets.TOKEN}}"
-          fi
-          export MISE_GITHUB_TOKEN="$GITHUB_TOKEN"
-          echo "$GITHUB_TOKEN" >> $GITHUB_ENV
-          echo "$MISE_GITHUB_TOKEN" >> $GITHUB_ENV
-
-      - name: Install mise
-        run: |
-          curl https://mise.run | sh
-          echo "$HOME/.local/bin" >> $GITHUB_PATH
-          echo "$HOME/.local/share/mise/bin" >> $GITHUB_PATH
-          echo "$HOME/.local/share/mise/shims" >> $GITHUB_PATH
-
-      - name: Install mise dependencies
-        run: |
-          mise install
-          mise list --local
-
-      - name: Check Lua formatting
-        run: mise run fmt:check
-
-      - name: Check for type-errors
-        run: mise run lint
-
-      - name: Run tests
-        run: mise run test:all

.gitignore

@@ -1,4 +1 @@
-.prefix/
 *.src.rock
-*.aider*
-luacov.*.out

.gitmodules

@@ -1,12 +0,0 @@
-[submodule "library/busted"]
-	path = library/busted
-	url = https://github.com/LuaCATS/busted
-	branch = main
-[submodule "library/luv"]
-	path = library/luv
-	url = https://github.com/LuaCATS/luv
-	branch = main
-[submodule "nvimv"]
-	path = nvimv
-	url = https://github.com/jrop/nvimv
-	branch = main

.luacov

@@ -1,6 +0,0 @@
-return {
-  include = {
-    'lua/u$',
-  },
-  tick = true,
-}

.styluaignore

@@ -1 +0,0 @@
-library/

Makefile

@@ -0,0 +1,15 @@
+PLENARY_DIR=~/.local/share/nvim/site/pack/test/opt/plenary.nvim
+
+all: lint test
+
+lint:
+	selene .
+
+fmt:
+	stylua .
+
+test: $(PLENARY_DIR)
+	NVIM_APPNAME=noplugstest nvim -u NORC --headless -c 'set packpath+=~/.local/share/nvim/site' -c 'packadd plenary.nvim' -c "PlenaryBustedDirectory spec/"
+
+$(PLENARY_DIR):
+	git clone https://github.com/nvim-lua/plenary.nvim/ $(PLENARY_DIR)

README.md

@@ -1,174 +1,265 @@
 # u.nvim
 
-Welcome to **u.nvim** - a Lua library for text manipulation in Neovim, focusing on
+Welcome to **u.nvim** – a powerful Lua library designed to enhance your text manipulation experience in NeoVim, focusing primarily on a context-aware "Range" utility. This utility allows you to work efficiently with text selections based on various conditions, in a variety of contexts, making coding and editing more intuitive and productive.
-range-based text operations, positions, and operator-pending mappings.
 
-This is a **single-file micro-library** meant to be vendored in your plugin or
+This is meant to be used as a **library**, not a plugin. On its own, `u.nvim` does nothing. It is meant to be used by plugin authors, to make their lives easier based on the variety of utilities I found I needed while growing my NeoVim config.
-config. On its own, `u.nvim` does nothing. It is meant to be used by plugin
-authors to make their lives easier. To get an idea of what a plugin built on
-top of `u.nvim` would look like, check out the [examples/](./examples/) directory.
 
 ## Features
 
-- **Range Utility**: Get context-aware selections with ease. Replace regions with
+- **Rendering System**: a utility that can declaratively render NeoVim-specific hyperscript into a buffer, supporting creating/managing extmarks, highlights, and key-event handling (requires NeoVim >0.11)
-  new text. Think of it as a programmatic way to work with visual selections.
+- **Signals**: a simple dependency tracking system that pairs well with the rendering utilities for creating reactive/interactive UIs in NeoVim.
-- **Position Utilities**: Work with cursor positions, marks, and extmarks.
+- **Range Utility**: Get context-aware selections with ease. Replace regions with new text. Think of it as a programmatic way to work with visual selections (or regions of text).
-- **Operator Key Mapping**: Flexible key mapping that works with motions.
+- **Code Writer**: Write code with automatic indentation and formatting.
-- **Text Object Definitions**: Define custom text objects easily.
+- **Operator Key Mapping**: Flexible key mapping that works with the selected text.
-- **User Command Helpers**: Create commands with range support.
+- **Text and Position Utilities**: Convenient functions to manage text objects and cursor positions.
-- **Repeat Utilities**: Dot-repeat support for custom operations.
 
 ### Installation
 
-This being a library, and not a proper plugin, it is recommended that you vendor
+lazy.nvim:
-the specific version of this library that you need, including it in your code.
+```lua
-Package managers are a developing landscape for Lua in the context of NeoVim.
+-- Setting `lazy = true` ensures that the library is only loaded
-Perhaps in the future, `lux` will eliminate the need to vendor this library in
+-- when `require 'u.<utility>' is called.
-your application code.
+{ 'jrop/u.nvim', lazy = true }
-
-#### If you are a Plugin Author
-
-Neovim does not have a good answer for automatic management of plugin dependencies. As such, it is recommended that library authors vendor u.nvim within their plugin. **u.nvim** is implemented in a single file, so this should be relatively painless. Furthermore, `lua/u.lua` versions are published into artifact tags `artifact-vX.Y.Z` as `init.lua` so that plugin authors can add u.nvim as a submodule to their plugin.
-
-<details>
-<summary>Example git submodule setup</summary>
-
-```bash
-# In your plugin repository
-git submodule add -- https://github.com/jrop/u.nvim lua/my_plugin/u
-cd lua/my_plugin/u/
-git checkout artifact-v0.2.0 # put whatever version of u.nvim you want to pin here
-# ... commit the submodule within your repo
-
-# This would place u.nvim@v0.2.0 at:
-# lua/my_plugin/u/init.lua
 ```
 
-Then in your plugin code:
+## Signal and Rendering Usage
 
-```lua
+### Overview
-local u = require('my_plugin.u')
 
-local Pos = u.Pos
+The Signal and Rendering mechanisms are two subsystems of u.nvim, that, while
-local Range = u.Range
+simplistic, [compose](./examples/counter.lua) [together](./examples/filetree.lua)
--- etc.
+[powerfully](./examples/picker.lua) to create a system for interactive and
-```
+responsive user interfaces. Here is a quick example that show-cases how easy it
-
+is to dive in to make any buffer an interactive UI:
-This approach allows plugin authors to:
-- Pin to specific versions of u.nvim
-- Get updates by pulling/committing new **u.nvim** versions (i.e., the usual git submodule way)
-- Keep the dependency explicit and version-controlled
-- Avoid namespace conflicts with user-installed plugins
-
-</details>
-
-#### If you are a User
-
-If you want to use u.nvim in your config directly:
 
 <details>
-<summary>vim.pack</summary>
+<summary>Example Code: counter.lua</summary>
 
 ```lua
-vim.pack.add { 'https://github.com/jrop/u.nvim' }
+local tracker = require 'u.tracker'
+local Buffer = require 'u.buffer'
+local h = require('u.renderer').h
+
+-- Create an buffer for the UI
+vim.cmd.vnew()
+local ui_buf = Buffer.current()
+ui_buf:set_tmp_options()
+
+local s_count = tracker.create_signal(0)
+
+-- Effect: Render
+-- Setup the effect for rendering the UI whenever dependencies are updated
+tracker.create_effect(function()
+  -- Calling `Signal:get()` in an effect registers the given signal as a
+  -- dependency of the current effect. Whenever that signal (or any other
+  -- dependency) changes, the effect will rerun. In this particular case,
+  -- rendering the UI is an effect that depends on one signal.
+  local count = s_count:get()
+
+  -- Markup is hyperscript, which is just 1) text, and 2) tags (i.e.,
+  -- constructed with `h(...)` calls). To help organize the markup, text and
+  -- tags can be nested in tables at any depth. Line breaks must be specified
+  -- manually, with '\n'.
+  ui_buf:render {
+    'Reactive Counter Example\n',
+    '========================\n\n',
+
+    { 'Counter: ', tostring(count), '\n' },
+
+    '\n',
+
+    {
+      h('text', {
+        hl = 'DiffDelete',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            vim.schedule(function()
+              s_count:update(function(n) return n - 1 end)
+            end)
+            -- Also equivalent: s_count:set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Decrement '),
+      ' ',
+      h('text', {
+        hl = 'DiffAdd',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            vim.schedule(function()
+              s_count:update(function(n) return n + 1 end)
+            end)
+            -- Also equivalent: s_count:set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Increment '),
+    },
+
+    '\n',
+    '\n',
+    { 'Press <CR> on each "button" above to increment/decrement the counter.' },
+  }
+end)
 ```
 
 </details>
 
-<details>
+### `u.tracker`
-<summary>lazy.nvim</summary>
+
+The `u.tracker` module provides a simple API for creating reactive variables. These can be composed in Effects and Memos utilizing Execution Contexts that track what signals are used by effects/memos.
 
 ```lua
+local tracker = require('u.tracker')
+
+local s_number = tracker.Signal:new(0)
+-- auto-compute the double of the number each time it changes:
+local s_doubled = tracker.create_memo(function() return s_number:get() * 2 end)
+tracker.create_effect(function()
+  local n = s_doubled:get()
+  -- ...
+  -- whenever s_doubled changes, this function gets run
+end)
+```
+
+**Note**: circular dependencies are **not** supported.
+
+### `u.renderer`
+
+The renderer library renders hyperscript into a buffer. Each render performs a
+minimal set of changes in order to transform the current buffer text into the
+desired state.
+
+**Hyperscript** is just 1) _text_ 2) `<text>` tags, which can be nested in 3) Lua tables for readability:
+
+```lua
+local h = require('u.renderer').h
+-- Hyperscript can be organized into tables:
 {
-  'jrop/u.nvim',
+  "Hello, ",
-  lazy = true,
+  {
+    "I am ", { "a" }, " nested table.",
+  },
+  '\n', -- newlines must be explicitly specified
+
+  -- booleans/nil are ignored:
+  some_conditional_flag and 'This text only shows when the flag is true',
+  -- e.g., use the above to show newlines in lists:
+  idx > 1 and '\n',
+
+  -- <text> tags are specified like so:
+  -- h('text', attributes, children)
+  h('text', {}, "I am a text node."),
+
+  -- <text> tags can be highlighted:
+  h('text', { hl = 'Comment' }, "I am highlighted."),
+
+  -- <text> tags can respond to key events:
+  h('text', {
+    hl = 'Keyword',
+    nmap = {
+      ["<CR>"] = function()
+        print("Hello World")
+        -- Return '' to swallow the event:
+        return ''
+      end,
+    },
+  }, "I am a text node."),
 }
 ```
 
-</details>
+Managing complex tables of hyperscript can be done more ergonomically using the
+`TreeBuilder` helper class:
 
+```lua
+local TreeBuilder = require('u.renderer').TreeBuilder
+
+-- ...
+renderer:render(
+  TreeBuilder.new()
+    -- text:
+    :put('some text')
+    -- hyperscript tables:
+    :put({ 'some text', 'more hyperscript' })
+    -- hyperscript tags:
+    :put_h('text', { --[[attributes]] }, { --[[children]] })
+    -- callbacks:
+    --- @param tb TreeBuilder
+    :nest(function(tb)
+      tb:put('some text')
+    end)
+    :tree()
+)
+```
+
+**Rendering**: The renderer library provides a `render` function that takes hyperscript in, and converts it to formatted buffer text:
+
+```lua
+local Renderer = require('u.renderer').Renderer
+local renderer = Renderer:new(0 --[[buffer number]])
+renderer:render {
+  -- ...hyperscript...
+}
+
+-- or, if you already have a buffer:
+local Buffer = require('u.buffer')
+local buf = Buffer.current()
+buf:render {
+  -- ...hyperscript...
+}
+```
 
 ## Range Usage
 
 ### A note on indices
 
-<blockquote>
+I love NeoVim. I am coming to love Lua. I don't like 1-based indices; perhaps I am too old. Perhaps I am too steeped in the history of loving the elegance of simple pointer arithmetic. Regardless, the way positions are addressed in NeoVim/Vim is (terrifyingly) mixed. Some methods return 1-based, others accept only 0-based. In order to stay sane, I had to make a choice to store everything in one, uniform representation in this library. I chose (what I humbly think is the only sane way) to stick with the tried-and-true 0-based index scheme. That abstraction leaks into the public API of this library.
-<del>
-I love NeoVim. I am coming to love Lua. I don't like 1-based indices; perhaps I
-am too old. Perhaps I am too steeped in the history of loving the elegance of
-simple pointer arithmetic. Regardless, the way positions are addressed in
-NeoVim/Vim is (terrifyingly) mixed. Some methods return 1-based, others accept
-only 0-based. In order to stay sane, I had to make a choice to store everything
-in one, uniform representation in this library. I chose (what I humbly think is
-the only sane way) to stick with the tried-and-true 0-based index scheme. That
-abstraction leaks into the public API of this library.
-</del>
-</blockquote>
-
-<br />
-<b>This has changed in v2</b>. After much thought, I realized that:
-
-1. The 0-based indexing in NeoVim is prevelant in the `:api`, which is designed
-   to be exposed to many languages. As such, it makes sense for this interface
-   to use 0-based indexing. However, many internal Vim functions use 1-based
-   indexing.
-2. This is a Lua library (surprise, surprise, duh) - the idioms of the language
-   should take precedence over my preference
-3. There were subtle bugs in the code where indices weren't being normalized to
-   0-based, anyways. Somehow it worked most of the time.
-
-As such, this library now uses 1-based indexing everywhere, doing the necessary
-interop conversions when calling `:api` functions.
 
 ### 1. Creating a Range
 
-The `Range` utility is the main feature of this library. Ranges can be constructed
+The `Range` utility is the main feature upon which most other things in this library are built, aside from a few standalone utilities. Ranges can be constructed manually, or preferably, obtained based on a variety of contexts.
-manually, or preferably, obtained based on a variety of contexts.
 
 ```lua
-local u = require 'u'
+local Range = require 'u.range'
+local start = Pos.new(0, 0, 0) -- Line 1, first column
+local stop = Pos.new(0, 2, 0) -- Line 3, first column
 
-local start = u.Pos.new(nil, 1, 1) -- Line 1, first column
+Range.new(start, stop, 'v') -- charwise selection
-local stop = u.Pos.new(nil, 3, 1)  -- Line 3, first column
+Range.new(start, stop, 'V') -- linewise selection
-
-u.Range.new(start, stop, 'v') -- charwise selection
-u.Range.new(start, stop, 'V') -- linewise selection
 ```
 
-This is usually not how you want to obtain a `Range`, however. Usually you want
+This is usually not how you want to obtain a `Range`, however. Usually you want to get the corresponding context of an edit operation and just "get me the current Range that represents this context".
-to get the corresponding context of an edit operation and just "get me the
-current Range that represents this context".
 
 ```lua
-local u = require 'u'
-
 -- get the first line in a buffer:
-u.Range.from_line(bufnr, 1)
+Range.from_line(0, 0)
 
 -- Text Objects (any text object valid in your configuration is supported):
 -- get the word the cursor is on:
-u.Range.from_motion('iw')
+Range.from_text_object('iw')
 -- get the WORD the cursor is on:
-u.Range.from_motion('iW')
+Range.from_text_object('iW')
 -- get the "..." the cursor is within:
-u.Range.from_motion('a"')
+Range.from_text_object('a"')
 
 -- Get the currently visually selected text:
--- NOTE: this does NOT work within certain contexts; more specialized utilities
+-- NOTE: this does NOT work within certain contexts; more specialized utilities are more appropriate in certain circumstances
--- are more appropriate in certain circumstances
+Range.from_vtext()
-u.Range.from_vtext()
 
 --
 -- Get the operated on text obtained from a motion:
 -- (HINT: use the opkeymap utility to make this less verbose)
 --
---- @param ty 'char'|'line'|'block'
+---@param ty 'char'|'line'|'block'
 function MyOpFunc(ty)
-  local range = u.Range.from_op_func(ty)
+  local range = Range.from_op_func(ty)
   -- do something with the range
 end
--- Try invoking this with: `<Leader>toaw`, and the current word will be the
+-- Try invoking this with: `<Leader>toaw`, and the current word will be the context:
--- context:
 vim.keymap.set('<Leader>to', function()
   vim.g.operatorfunc = 'v:lua.MyOpFunc'
   return 'g@'
@@ -177,10 +268,9 @@ end, { expr = true })
 --
 -- Commands:
 --
--- When executing commands in a visual context, getting the selected text has
+-- When executing commands in a visual context, getting the selected text has to be done differently:
--- to be done differently:
 vim.api.nvim_create_user_command('MyCmd', function(args)
-  local range = u.Range.from_cmd_args(args)
+  local range = Range.from_cmd_args(args)
   if range == nil then
     -- the command was executed in normal mode
   else
@@ -189,15 +279,14 @@ vim.api.nvim_create_user_command('MyCmd', function(args)
 end, { range = true })
 ```
 
-So far, that's a lot of ways to _get_ a `Range`. But what can you do with a
+So far, that's a lot of ways to _get_ a `Range`. But what can you do with a range once you have one? Plenty, it turns out!
-range once you have one? Plenty, it turns out!
 
 ```lua
 local range = ...
 range:lines() -- get the lines in the range's region
 range:text() -- get the text (i.e., string) in the range's region
-range:line(1) -- get the first line within this range
+range:line0(0) -- get the first line within this range
-range:line(-1) -- get the last line within this range
+range:line0(-1) -- get the last line within this range
 -- replace with new contents:
 range:replace {
   'replacement line 1',
@@ -213,143 +302,74 @@ range:replace(nil)
 Define custom (dot-repeatable) key mappings for text objects:
 
 ```lua
-local u = require 'u'
+local opkeymap = require 'u.opkeymap'
 
 -- invoke this function by typing, for example, `<leader>riw`:
 -- `range` will contain the bounds of the motion `iw`.
-u.opkeymap('n', '<leader>r', function(range)
+opkeymap('n', '<leader>r', function(range)
   print(range:text()) -- Prints the text within the selected range
 end)
 ```
 
-### 3. Utility Functions
+### 3. Working with Code Writer
+
+To write code with indentation, use the `CodeWriter` class:
+
+```lua
+local CodeWriter = require 'u.codewriter'
+local cw = CodeWriter.new()
+cw:write('{')
+cw:indent(function(innerCW)
+  innerCW:write('x: 123')
+end)
+cw:write('}')
+```
+
+### 4. Utility Functions
 
 #### Custom Text Objects
 
-Simply by returning a `Range`, you can easily define your own text objects:
+Simply by returning a `Range` or a `Pos`, you can easily and quickly define
+your own text objects:
 
 ```lua
-local u = require 'u'
+local utils = require 'u.utils'
+local Range = require 'u.range'
 
 -- Select whole file:
-u.define_txtobj('ag', function()
+utils.define_text_object('ag', function()
-  return u.Range.from_buf_text()
+  return Range.from_buf_text()
-end)
-
--- Select content inside nearest quotes:
-u.define_txtobj('iq', function()
-  return u.Range.find_nearest_quotes()
-end)
-
--- Select content inside nearest brackets:
-u.define_txtobj('ib', function()
-  return u.Range.find_nearest_brackets()
 end)
 ```
 
-#### User Commands with Range Support
+#### Buffer Management
 
-Create user commands that work with visual selections:
+Access and manipulate buffers easily:
 
 ```lua
-local u = require 'u'
+local Buffer = require 'u.buffer'
-
+local buf = Buffer.current()
-u.ucmd('MyCmd', function(args)
+buf:line_count() -- the number of lines in the current buffer
-  if args.info then
+buf:get_option '...'
-    -- args.info is a Range representing the selection
+buf:set_option('...', ...)
-    print('Selected text:', args.info:text())
+buf:get_var '...'
-  else
+buf:set_var('...', ...)
-    -- No range provided
+buf:all() -- returns a Range representing the entire buffer
-    print('No selection')
+buf:is_empty() -- returns true if the buffer has no text
-  end
+buf:append_line '...'
-end, { range = true })
+buf:line0(0) -- returns a Range representing the first line in the buffer
+buf:line0(-1) -- returns a Range representing the last line in the buffer
+buf:lines(0, 1) -- returns a Range representing the first two lines in the buffer
+buf:lines(1, -2) -- returns a Range representing all but the first and last lines of a buffer
+buf:text_object('iw') -- returns a Range representing the text object 'iw' in the give buffer
 ```
 
-#### Repeat Utilities
-
-Enable dot-repeat for custom operations:
-
-```lua
-local u = require 'u'
-
--- Call this in your plugin's setup:
-u.repeat_.setup()
-
--- Then use in your operations:
-u.repeat_.run_repeatable(function()
-  -- Your mutation here
-  -- This will be repeatable with '.'
-end)
-```
-
-## API Reference
-
-### `u.Pos`
-
-Position class representing a location in a buffer.
-
-```lua
-local pos = u.Pos.new(bufnr, lnum, col, off)
-pos:next(1)      -- next position (forward)
-pos:next(-1)     -- previous position (backward)
-pos:char()       -- character at position
-pos:line()       -- line text
-pos:eol()        -- end of line position
-pos:save_to_cursor() -- move cursor to position
-```
-
-### `u.Range`
-
-Range class representing a text region.
-
-```lua
-local range = u.Range.new(start, stop, mode)
-range:text()     -- get text content
-range:lines()    -- get lines as array
-range:replace(text) -- replace with new text
-range:contains(pos) -- check if position is within range
-range:shrink(n)  -- shrink range by n characters from each side
-range:highlight('Search') -- highlight range temporarily
-```
-
-### `u.opkeymap(mode, lhs, rhs, opts)`
-
-Create operator-pending keymaps.
-
-### `u.define_txtobj(key_seq, fn, opts)`
-
-Define custom text objects.
-
-### `u.ucmd(name, cmd, opts)`
-
-Create user commands with enhanced range support.
-
-### `u.create_delegated_cmd_args(args)`
-
-Create arguments for delegating between commands.
-
-### `u.repeat_`
-
-Module for dot-repeat support.
-
 ## License (MIT)
 
 Copyright (c) 2024 jrapodaca@gmail.com
 
-Permission is hereby granted, free of charge, to any person obtaining a copy of
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
-this software and associated documentation files (the "Software"), to deal in
-the Software without restriction, including without limitation the rights to
-use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
-of the Software, and to permit persons to whom the Software is furnished to do
-so, subject to the following conditions:
 
-The above copyright notice and this permission notice shall be included in all
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
-copies or substantial portions of the Software.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.

examples/counter.lua

@@ -0,0 +1,65 @@
+local tracker = require 'u.tracker'
+local Buffer = require 'u.buffer'
+local h = require('u.renderer').h
+
+-- Create an buffer for the UI
+vim.cmd.vnew()
+local ui_buf = Buffer.current()
+ui_buf:set_tmp_options()
+
+local s_count = tracker.create_signal(0, 'counter_signal')
+
+-- Effect: Render
+-- Setup the effect for rendering the UI whenever dependencies are updated
+tracker.create_effect(function()
+  -- Calling `Signal:get()` in an effect registers the given signal as a
+  -- dependency of the current effect. Whenever that signal (or any other
+  -- dependency) changes, the effect will rerun. In this particular case,
+  -- rendering the UI is an effect that depends on one signal.
+  local count = s_count:get()
+
+  -- Markup is hyperscript, which is just 1) text, and 2) tags (i.e.,
+  -- constructed with `h(...)` calls). To help organize the markup, text and
+  -- tags can be nested in tables at any depth. Line breaks must be specified
+  -- manually, with '\n'.
+  ui_buf:render {
+    'Reactive Counter Example\n',
+    '========================\n\n',
+
+    { 'Counter: ', tostring(count), '\n' },
+
+    '\n',
+
+    {
+      h('text', {
+        hl = 'DiffDelete',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            s_count:schedule_update(function(n) return n - 1 end)
+            -- Also equivalent: s_count:schedule_set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Decrement '),
+      ' ',
+      h('text', {
+        hl = 'DiffAdd',
+        nmap = {
+          ['<CR>'] = function()
+            -- Update the contents of the s_count signal, notifying any
+            -- dependencies (in this case, the render effect):
+            s_count:schedule_update(function(n) return n + 1 end)
+            -- Also equivalent: s_count:schedule_set(s_count:get() - 1)
+            return ''
+          end,
+        },
+      }, ' Increment '),
+    },
+
+    '\n',
+    '\n',
+    { 'Press <CR> on each "button" above to increment/decrement the counter.' },
+  }
+end)

examples/filetree.lua

@@ -0,0 +1,442 @@
+--------------------------------------------------------------------------------
+-- File Tree Viewer Module
+--
+-- Future Enhancements:
+-- - Consider implementing additional features like searching for files,
+--   filtering displayed nodes, or adding support for more file types.
+-- - Improve user experience with customizable UI elements and enhanced
+--   navigation options.
+-- - Implement a file watcher to automatically update the file tree when files
+--   change on the underlying filesystem.
+--------------------------------------------------------------------------------
+
+--- @alias FsDir { kind: 'dir'; path: string; expanded: boolean; children: FsNode[] }
+--- @alias FsFile { kind: 'file'; path: string }
+--- @alias FsNode FsDir | FsFile
+--- @alias ShowOpts { root_path?: string, width?: number, focus_path?: string }
+
+local Buffer = require 'u.buffer'
+local Renderer = require('u.renderer').Renderer
+local TreeBuilder = require('u.renderer').TreeBuilder
+local h = require('u.renderer').h
+local tracker = require 'u.tracker'
+
+local M = {}
+local H = {}
+
+--------------------------------------------------------------------------------
+-- Helpers:
+--------------------------------------------------------------------------------
+
+--- Splits the given path into a list of path components.
+--- @param path string
+function H.split_path(path)
+  local parts = {}
+  local curr = path
+  while #curr > 0 and curr ~= '.' and curr ~= '/' do
+    table.insert(parts, 1, vim.fs.basename(curr))
+    curr = vim.fs.dirname(curr)
+  end
+  return parts
+end
+
+--- Normalizes the given path to an absolute path.
+--- @param path string
+function H.normalize(path)
+  path = vim.fs.normalize(path)
+  if path:sub(1, 1) ~= '/' then path = vim.fs.joinpath(vim.uv.cwd(), path) end
+  return vim.fs.normalize(path)
+end
+
+--- Computes the relative path from `base` to `path`.
+--- @param path string
+--- @param base string
+function H.relative(path, base)
+  path = H.normalize(path)
+  base = H.normalize(base)
+  if path:sub(1, #base) == base then path = path:sub(#base + 1) end
+  if vim.startswith(path, '/') then path = path:sub(2) end
+  return path
+end
+
+--- @param root_path string
+--- @return { tree: FsDir; path_to_node: table<string, FsNode> }
+function H.get_tree_inf(root_path)
+  --- @type table<string, FsNode>
+  local path_to_node = {}
+
+  --- @type FsDir
+  local tree = {
+    kind = 'dir',
+    path = H.normalize(root_path or '.'),
+    expanded = true,
+    children = {},
+  }
+  path_to_node[tree.path] = tree
+
+  H.populate_dir_children(tree, path_to_node)
+  return { tree = tree, path_to_node = path_to_node }
+end
+
+--- @param tree FsDir
+--- @param path_to_node table<string, FsNode>
+function H.populate_dir_children(tree, path_to_node)
+  tree.children = {}
+
+  for child_path, kind in vim.iter(vim.fs.dir(tree.path, { depth = 1 })) do
+    child_path = H.normalize(vim.fs.joinpath(tree.path, child_path))
+    local prev_node = path_to_node[child_path]
+
+    if kind == 'directory' then
+      local new_node = {
+        kind = 'dir',
+        path = child_path,
+        expanded = prev_node and prev_node.expanded or false,
+        children = {},
+      }
+      path_to_node[new_node.path] = new_node
+      table.insert(tree.children, new_node)
+    else
+      local new_node = {
+        kind = 'file',
+        path = child_path,
+      }
+      path_to_node[new_node.path] = new_node
+      table.insert(tree.children, new_node)
+    end
+  end
+
+  table.sort(tree.children, function(a, b)
+    -- directories first:
+    if a.kind ~= b.kind then return a.kind == 'dir' end
+    return a.path < b.path
+  end)
+end
+
+--- @param opts {
+---   bufnr: number;
+---   prev_winnr: number;
+---   root_path: string;
+---   focus_path?: string;
+--- }
+---
+--- @return { expand: fun(path: string), collapse: fun(path: string) }
+local function _render_in_buffer(opts)
+  local winnr = vim.api.nvim_buf_call(opts.bufnr, function() return vim.api.nvim_get_current_win() end)
+  local s_tree_inf = tracker.create_signal(H.get_tree_inf(opts.root_path))
+  local s_focused_path = tracker.create_signal(H.normalize(opts.focus_path or opts.root_path))
+
+  tracker.create_effect(function()
+    local focused_path = s_focused_path:get()
+
+    s_tree_inf:update(function(tree_inf)
+      local parts = H.split_path(H.relative(focused_path, tree_inf.tree.path))
+      local path_to_node = tree_inf.path_to_node
+
+      --- @param node FsDir
+      --- @param child_names string[]
+      local function expand_to(node, child_names)
+        if #child_names == 0 then return end
+        node.expanded = true
+
+        local next_child_name = table.remove(child_names, 1)
+        for _, child in ipairs(node.children) do
+          if child.kind == 'dir' and vim.fs.basename(child.path) == next_child_name then
+            H.populate_dir_children(child, path_to_node)
+            expand_to(child, child_names)
+          end
+        end
+      end
+      expand_to(tree_inf.tree, parts)
+      return tree_inf
+    end)
+  end)
+
+  -- --
+  -- -- TODO: :help watch-file
+  -- --
+  -- local watcher = vim.uv.new_fs_event()
+  -- if watcher ~= nil then
+  --   watcher:start(root_path, { recursive = true }, function(err, fname, status)
+  --     -- TODO: more efficient update:
+  --     s_tree_inf:set(H.get_tree(root_path))
+  --
+  --     -- TODO: proper disposal
+  --     watcher:stop()
+  --   end)
+  -- end
+
+  local controller = {}
+
+  --- @param path string
+  function controller.focus_path(path) s_focused_path:set(H.normalize(path)) end
+
+  function controller.refresh() s_tree_inf:set(H.get_tree_inf(opts.root_path)) end
+
+  --- @param path string
+  function controller.expand(path)
+    path = H.normalize(path)
+    local path_to_node = s_tree_inf:get().path_to_node
+
+    local node = path_to_node[path]
+    if node == nil then return end
+
+    if node.kind == 'dir' then
+      s_tree_inf:update(function(tree_inf2)
+        H.populate_dir_children(node, path_to_node)
+        tree_inf2.path_to_node[node.path].expanded = true
+        return tree_inf2
+      end)
+      if #node.children == 0 then
+        s_focused_path:set(node.path)
+      else
+        s_focused_path:set(node.children[1].path)
+      end
+    else
+      if node.kind == 'file' then
+        -- open file:
+        vim.api.nvim_win_call(opts.prev_winnr, function() vim.cmd.edit(node.path) end)
+        vim.api.nvim_set_current_win(opts.prev_winnr)
+      end
+    end
+  end
+
+  --- @param path string
+  function controller.collapse(path)
+    path = H.normalize(path)
+    local path_to_node = s_tree_inf:get().path_to_node
+
+    local node = path_to_node[path]
+    if node == nil then return end
+
+    if node.kind == 'dir' then
+      if node.expanded then
+        -- collapse self/node:
+        s_focused_path:set(node.path)
+        s_tree_inf:update(function(tree_inf2)
+          tree_inf2.path_to_node[node.path].expanded = false
+          return tree_inf2
+        end)
+      else
+        -- collapse parent:
+        local parent_dir = path_to_node[vim.fs.dirname(node.path)]
+        if parent_dir ~= nil then
+          s_focused_path:set(parent_dir.path)
+          s_tree_inf:update(function(tree_inf2)
+            tree_inf2.path_to_node[parent_dir.path].expanded = false
+            return tree_inf2
+          end)
+        end
+      end
+    elseif node.kind == 'file' then
+      local parent_dir = path_to_node[vim.fs.dirname(node.path)]
+      if parent_dir ~= nil then
+        s_focused_path:set(parent_dir.path)
+        s_tree_inf:update(function(tree_inf2)
+          tree_inf2.path_to_node[parent_dir.path].expanded = false
+          return tree_inf2
+        end)
+      end
+    end
+  end
+
+  --- @param root_path string
+  function controller.new(root_path)
+    vim.ui.input({
+      prompt = 'New: ',
+      completion = 'file',
+    }, function(input)
+      if input == nil then return end
+      local new_path = vim.fs.joinpath(root_path, input)
+
+      if vim.endswith(input, '/') then
+        -- Create a directory:
+        vim.fn.mkdir(new_path, input, 'p')
+      else
+        -- Create a file:
+
+        -- First, make sure the parent directory exists:
+        vim.fn.mkdir(vim.fs.dirname(new_path), 'p')
+
+        -- Now create an empty file:
+        local uv = vim.loop or vim.uv
+        local fd = uv.fs_open(new_path, 'w', 438)
+        if fd then uv.fs_write(fd, '') end
+      end
+
+      controller.refresh()
+      controller.focus_path(new_path)
+    end)
+  end
+
+  --- @param path string
+  function controller.rename(path)
+    path = H.normalize(path)
+    local root_path = vim.fs.dirname(path)
+    vim.ui.input({
+      prompt = 'Rename: ',
+      default = vim.fs.basename(path),
+      completion = 'file',
+    }, function(input)
+      if input == nil then return end
+
+      local new_path = vim.fs.joinpath(root_path, input);
+      (vim.loop or vim.uv).fs_rename(path, new_path)
+      controller.refresh()
+      controller.focus_path(new_path)
+    end)
+  end
+
+  --
+  -- Render:
+  --
+  local renderer = Renderer.new(opts.bufnr)
+  tracker.create_effect(function()
+    --- @type { tree: FsDir; path_to_node: table<string, FsNode> }
+    local tree_inf = s_tree_inf:get()
+    local tree = tree_inf.tree
+
+    --- @type string
+    local focused_path = s_focused_path:get()
+
+    --- As we render the tree, keep track of what line each node is on, so that
+    --- we have an easy way to make the cursor jump to each node (i.e., line)
+    --- at will:
+    --- @type table<string, number>
+    local node_lines = {}
+    local current_line = 0
+
+    --- The UI is rendered as a list of hypserscript elements:
+    local tb = TreeBuilder.new()
+
+    --- Since the filesystem is a recursive tree of nodes, we need to
+    --- recursively render each node. This function does just that:
+    --- @param node FsNode
+    --- @param level number
+    local function render_node(node, level)
+      local name = vim.fs.basename(node.path)
+      current_line = current_line + 1
+      node_lines[node.path] = current_line
+
+      local nmaps = {
+        h = function()
+          vim.schedule(function() controller.collapse(node.path) end)
+          return ''
+        end,
+        l = function()
+          vim.schedule(function() controller.expand(node.path) end)
+          return ''
+        end,
+        n = function()
+          vim.schedule(function() controller.new(node.kind == 'file' and vim.fs.dirname(node.path) or node.path) end)
+          return ''
+        end,
+        r = function()
+          vim.schedule(function() controller.rename(node.path) end)
+          return ''
+        end,
+        y = function()
+          vim.fn.setreg([["]], H.relative(node.path, tree.path))
+          return ''
+        end,
+      }
+
+      if node.kind == 'dir' then
+        --
+        -- Render a directory node:
+        --
+        local icon = node.expanded and '' or ''
+        tb:put {
+          current_line > 1 and '\n',
+          h('text', { hl = 'Constant', nmap = nmaps }, { string.rep('  ', level), icon, ' ', name }),
+        }
+        if node.expanded then
+          for _, child in ipairs(node.children) do
+            render_node(child, level + 1)
+          end
+        end
+      elseif node.kind == 'file' then
+        tb:put {
+          current_line > 1 and '\n',
+          h('text', { nmap = nmaps }, { string.rep('  ', level), '󰈔 ', name }),
+        }
+      end
+    end
+    render_node(tree, 0)
+
+    -- The following modifies buffer contents, so it needs to be scheduled:
+    vim.schedule(function()
+      renderer:render(tb:tree())
+
+      local cpos = vim.api.nvim_win_get_cursor(winnr)
+      pcall(vim.api.nvim_win_set_cursor, winnr, { node_lines[focused_path], cpos[2] })
+    end)
+  end, 's:tree')
+
+  return controller
+end
+
+--------------------------------------------------------------------------------
+-- Public API functions:
+--------------------------------------------------------------------------------
+
+--- @type {
+---   bufnr: number;
+---   winnr: number;
+---   controller: { expand: fun(path: string), collapse: fun(path: string) };
+--- } | nil
+local current_inf = nil
+
+--- Show the filetree:
+--- @param opts? ShowOpts
+function M.show(opts)
+  if current_inf ~= nil then return current_inf.controller end
+  opts = opts or {}
+
+  local prev_winnr = vim.api.nvim_get_current_win()
+
+  vim.cmd 'vnew'
+  local buf = Buffer.from_nr(vim.api.nvim_get_current_buf())
+  buf:set_tmp_options()
+
+  local winnr = vim.api.nvim_get_current_win()
+  vim.api.nvim_feedkeys(vim.api.nvim_replace_termcodes('<C-w>H', true, true, true), 'x', false)
+  vim.api.nvim_win_set_width(0, opts.width or 30)
+  vim.api.nvim_create_autocmd('WinClosed', {
+    once = true,
+    pattern = tostring(winnr),
+    callback = M.hide,
+  })
+
+  vim.wo.number = false
+  vim.wo.relativenumber = false
+
+  local bufnr = vim.api.nvim_get_current_buf()
+
+  local controller = _render_in_buffer(vim.tbl_extend('force', opts, {
+    bufnr = bufnr,
+    prev_winnr = prev_winnr,
+    root_path = opts.root_path or H.normalize '.',
+  }))
+  current_inf = { bufnr = bufnr, winnr = winnr, controller = controller }
+  return controller
+end
+
+--- Hide the filetree:
+function M.hide()
+  if current_inf == nil then return end
+  pcall(vim.cmd.bdelete, current_inf.bufnr)
+  current_inf = nil
+end
+
+--- Toggle the filetree:
+--- @param opts? ShowOpts
+function M.toggle(opts)
+  if current_inf == nil then
+    M.show(opts)
+  else
+    M.hide()
+  end
+end
+
+return M

examples/matcher.lua

@@ -1,51 +0,0 @@
---
--- Bracket matcher: highlights the nearest matching pair of brackets (like MatchParen)
--- when the cursor is near them. Updates dynamically on CursorMoved in normal mode.
---
-local u = require 'u'
-local Range = u.Range
-
-local M = {}
-
---- @type { clear: fun() }[]
-local HIGHLIGHTS = {}
-local LAST_RANGE = nil
-
-local function clear_highlights()
-  for _, hl in ipairs(HIGHLIGHTS) do
-    hl.clear()
-  end
-  HIGHLIGHTS = {}
-end
-
-local function update()
-  local mode = vim.fn.mode():sub(1, 1)
-  if mode ~= 'n' then return end
-
-  local last_range = LAST_RANGE
-  local bracket_range = Range.find_nearest_brackets()
-  LAST_RANGE = bracket_range
-
-  if not bracket_range then return clear_highlights() end
-  if bracket_range == last_range then return end
-
-  clear_highlights()
-
-  local open = Range.new(bracket_range.start, bracket_range.start, 'v')
-  local close = Range.new(bracket_range.stop, bracket_range.stop, 'v')
-
-  HIGHLIGHTS = {
-    open:highlight('MatchParen', { priority = 999 }),
-    close:highlight('MatchParen', { priority = 999 }),
-  }
-end
-
-function M.setup()
-  local group = vim.api.nvim_create_augroup('Matcher', { clear = true })
-  vim.api.nvim_create_autocmd({ 'CursorMoved' }, {
-    group = group,
-    callback = update,
-  })
-end
-
-return M

examples/picker.lua

@@ -0,0 +1,874 @@
+local utils = require 'u.utils'
+local Buffer = require 'u.buffer'
+local Renderer = require('u.renderer').Renderer
+local h = require('u.renderer').h
+local TreeBuilder = require('u.renderer').TreeBuilder
+local tracker = require 'u.tracker'
+
+local M = {}
+
+local S_EDITOR_DIMENSIONS = tracker.create_signal(utils.get_editor_dimensions(), 's:editor_dimensions')
+vim.api.nvim_create_autocmd('VimResized', {
+  callback = function()
+    local new_dim = utils.get_editor_dimensions()
+    S_EDITOR_DIMENSIONS:set(new_dim)
+  end,
+})
+
+--- @param low number
+---@param x number
+---@param high number
+local function clamp(low, x, high)
+  x = math.max(low, x)
+  x = math.min(x, high)
+  return x
+end
+
+--- @generic T
+--- @param arr `T`[]
+--- @return T[]
+local function shallow_copy_arr(arr) return vim.iter(arr):totable() end
+
+--------------------------------------------------------------------------------
+-- BEGIN create_picker
+--
+-- This is the star of the show (in this file, anyway).
+-- In summary, the outline of this function is:
+-- 1. Setup signals/memos for computing the picker size, and window positions
+-- 2. Create the two windows:
+--   a. The picker input. This is where the filter is typed
+--   b. The picker list. This is where the items are displayed
+-- 3. Setup event handlers that respond to user input
+-- 4. Render the list. After all the prework above, this is probably the
+--    shortest portion of this function.
+--------------------------------------------------------------------------------
+
+--- @alias SelectController {
+---   get_items: fun(): T[];
+---   set_items: fun(items: T[]);
+---   set_filter_text: fun(filter_text: string);
+---   get_selected_indices: fun(): number[];
+---   get_selected_items: fun(): T[];
+---   set_selected_indices: fun(indicies: number[], ephemeral?: boolean);
+---   close: fun();
+--- }
+--- @alias SelectOpts<T> {
+---   items: `T`[];
+---   multi?: boolean;
+---   format_item?: fun(item: T[]): Tree;
+---   on_finish?: fun(items: T[], indicies: number[]);
+---   on_selection_changed?: fun(items: T[], indicies: number[]);
+---   mappings?: table<string, fun(select: SelectController)>;
+--- }
+
+--- @generic T
+--- @param opts SelectOpts<T>
+function M.create_picker(opts)
+  local is_in_insert_mode = vim.api.nvim_get_mode().mode:sub(1, 1) == 'i'
+  local stopinsert = not is_in_insert_mode
+
+  if opts.multi == nil then opts.multi = false end
+
+  local H = {}
+
+  --- Runs a function `fn`, and if it fails, cleans up the UI by calling
+  --- `H.finish`
+  ---
+  --- @generic T
+  --- @param fn fun(): `T`
+  --- @return T
+  local function safe_run(fn, ...)
+    local ok, result_or_error = pcall(fn, ...)
+    if not ok then
+      pcall(H.finish, true, result_or_error)
+      error(result_or_error .. '\n' .. debug.traceback())
+    end
+    return result_or_error
+  end
+
+  --- Creates a function that safely calls the given function, cleaning up the
+  --- UI if it ever fails
+  ---
+  --- @generic T
+  --- @param fn `T`
+  --- @return T
+  local function safe_wrap(fn)
+    return function(...) return safe_run(fn, ...) end
+  end
+
+  --
+  -- Compute the positions of the input bar and the list:
+  --
+
+  -- Reactively compute the space available for the picker based on the size of
+  -- the editor
+  local s_editor_dimensions = S_EDITOR_DIMENSIONS:clone()
+  local s_picker_space_available = tracker.create_memo(safe_wrap(function()
+    local editor_dim = s_editor_dimensions:get()
+    local width = math.floor(editor_dim.width * 0.75)
+    local height = math.floor(editor_dim.height * 0.75)
+    local row = math.floor((editor_dim.height - height) / 2)
+    local col = math.floor((editor_dim.width - width) / 2)
+    return { width = width, height = height, row = row, col = col }
+  end))
+
+  -- Reactively compute the size of the prompt (input) bar
+  local s_w_input_coords = tracker.create_memo(safe_wrap(function()
+    local picker_coords = s_picker_space_available:get()
+    return {
+      width = picker_coords.width,
+      height = 1,
+      row = picker_coords.row,
+      col = picker_coords.col,
+    }
+  end))
+
+  -- Reactively compute the size of the list view
+  local s_w_list_coords = tracker.create_memo(safe_wrap(function()
+    local picker_coords = s_picker_space_available:get()
+    return {
+      width = picker_coords.width,
+      height = picker_coords.height - 3,
+      row = picker_coords.row + 3,
+      col = picker_coords.col,
+    }
+  end))
+
+  --
+  -- Create resources (i.e., windows):
+  --
+
+  local w_input_cfg = {
+    width = s_w_input_coords:get().width,
+    height = s_w_input_coords:get().height,
+    row = s_w_input_coords:get().row,
+    col = s_w_input_coords:get().col,
+    relative = 'editor',
+    focusable = true,
+    border = 'rounded',
+  }
+  local w_input_buf = Buffer.create(false, true)
+  local w_input = vim.api.nvim_open_win(w_input_buf.buf, false, w_input_cfg)
+  vim.wo[w_input].number = false
+  vim.wo[w_input].relativenumber = false
+
+  -- The following option is a signal to other plugins like 'cmp' to not mess
+  -- with this buffer:
+  vim.bo[w_input_buf.buf].buftype = 'prompt'
+  vim.fn.prompt_setprompt(w_input_buf.buf, '')
+
+  vim.api.nvim_set_current_win(w_input)
+  tracker.create_effect(safe_wrap(function()
+    -- update window position/size every time the editor is resized:
+    w_input_cfg = vim.tbl_deep_extend('force', w_input_cfg, s_w_input_coords:get())
+    vim.api.nvim_win_set_config(w_input, w_input_cfg)
+  end))
+
+  local w_list_cfg = {
+    width = s_w_list_coords:get().width,
+    height = s_w_list_coords:get().height,
+    row = s_w_list_coords:get().row,
+    col = s_w_list_coords:get().col,
+    relative = 'editor',
+    focusable = true,
+    border = 'rounded',
+  }
+  local w_list_buf = Buffer.create(false, true)
+  local w_list = vim.api.nvim_open_win(w_list_buf.buf, false, w_list_cfg)
+  vim.wo[w_list].number = false
+  vim.wo[w_list].relativenumber = false
+  vim.wo[w_list].scrolloff = 0
+  tracker.create_effect(safe_wrap(function()
+    -- update window position/size every time the editor is resized:
+    w_list_cfg = vim.tbl_deep_extend('force', w_list_cfg, s_w_list_coords:get())
+    vim.api.nvim_win_set_config(w_list, w_list_cfg)
+  end))
+
+  -- Now that we have created the window with the prompt in it, start insert
+  -- mode so that the user can type immediately:
+  vim.cmd.startinsert()
+
+  --
+  -- State:
+  --
+
+  local s_items_raw = tracker.create_signal(opts.items, 's:items')
+  local s_items = s_items_raw:debounce(100)
+  local s_selected_indices = tracker.create_signal({}, 's:selected_indices')
+  local s_top_offset = tracker.create_signal(0, 's:top_offset')
+  local s_cursor_index = tracker.create_signal(1, 's:cursor_index')
+
+  local s_filter_text_undebounced = tracker.create_signal('', 's:filter_text')
+  w_input_buf:autocmd('TextChangedI', {
+    callback = safe_wrap(function() s_filter_text_undebounced:set(vim.api.nvim_get_current_line()) end),
+  })
+  local s_filter_text = s_filter_text_undebounced:debounce(50)
+
+  --
+  -- Derived State:
+  --
+
+  local s_formatted_items = tracker.create_memo(function()
+    local function _format_item(item) return opts.format_item and opts.format_item(item) or tostring(item) end
+
+    local items = s_items:get()
+    return vim.iter(items):map(function(item) return { item = item, formatted = _format_item(item) } end):totable()
+  end)
+
+  -- When the filter text changes, update the filtered items:
+  local s_filtered_items = tracker.create_memo(
+    safe_wrap(function()
+      local formatted_items = s_formatted_items:get()
+      local filter_text = vim.trim(s_filter_text:get())
+      local filter_pattern = (#formatted_items > 250 and #filter_text <= 3) and (filter_text:gsub('%.', '%%.'))
+        or vim.iter(vim.split(filter_text, '')):map(function(c) return c .. '.*' end):join ''
+
+      local new_filtered_items = vim
+        .iter(formatted_items)
+        :enumerate()
+        :map(function(i, inf) return { orig_idx = i, item = inf.item, formatted = inf.formatted } end)
+        :filter(function(inf)
+          if filter_text == '' then return true end
+          local formatted_as_string = Renderer.markup_to_string { tree = inf.formatted }
+          local match = string.match(Renderer.markup_to_string { tree = formatted_as_string }, filter_pattern)
+          return match ~= nil
+        end)
+        :totable()
+
+      -- Don't do the levenshtein-sort if there are over 250 items:
+      if #new_filtered_items <= 250 then
+        table.sort(new_filtered_items, function(a_inf, b_inf)
+          local a = Renderer.markup_to_string { markup = a_inf.formatted }
+          local b = Renderer.markup_to_string { markup = b_inf.formatted }
+          if a == b then return false end
+
+          local lev_a = utils.levenshtein(vim.split(filter_text, ''), vim.split(a, ''))
+          local lev_b = utils.levenshtein(vim.split(filter_text, ''), vim.split(b, ''))
+          return #lev_a < #lev_b
+        end)
+      end
+
+      s_top_offset:set(0)
+      s_cursor_index:set(1)
+      return new_filtered_items
+    end),
+    'e:(filter_text=>filtered_items)'
+  )
+
+  -- Visible items, are _just_ the items that fit into the current viewport.
+  -- This is an optimization so that we are not rendering thousands of lines of
+  -- items on each state-change.
+  local s_visible_items = tracker.create_memo(
+    safe_wrap(function()
+      return vim
+        .iter(s_filtered_items:get())
+        :enumerate()
+        :skip(s_top_offset:get())
+        :take(s_w_list_coords:get().height)
+        :map(
+          function(i, inf)
+            return {
+              filtered_idx = i,
+              orig_idx = inf.orig_idx,
+              item = inf.item,
+              formatted = inf.formatted,
+            }
+          end
+        )
+        :totable()
+    end),
+    'm:visible_items'
+  )
+
+  -- Track selection information:
+  local s_selection_info = tracker.create_memo(
+    safe_wrap(function()
+      local items = s_items:get()
+      local selected_indices = s_selected_indices:get()
+      --- @type { orig_idx: number; item: T }[]
+      local filtered_items = s_filtered_items:get()
+      local cursor_index = s_cursor_index:get()
+      local indices = shallow_copy_arr(selected_indices) -- shallow copy
+      if #indices == 0 and #filtered_items > 0 then indices = { filtered_items[cursor_index].orig_idx } end
+      return {
+        items = vim.iter(indices):map(function(i) return items[i] end):totable(),
+        indices = indices,
+      }
+    end),
+    'm:selection_info'
+  )
+
+  --- When it is time to close the picker, this is the main cleanup routine
+  --- that runs in all cases:
+  ---
+  --- @param esc? boolean Whether the user pressed <Esc> or not
+  --- @param err? any Any error that occurred
+  function H.finish(esc, err)
+    -- s_editor_dimensions is the only signal that is cloned from a global,
+    -- one. It is therefore the only one that needs to be manually disposed.
+    -- The other ones should get cleaned up by the GC
+    s_editor_dimensions:dispose()
+    -- If we happen to have any async state-changes coming down the pipeline,
+    -- we can say right now that we are done rendering new UI (to avoid
+    -- "invalid window ID" errors):
+    H.unsubscribe_render_effect()
+    -- buftype=prompt buffers are not "temporary", so delete the buffer manually:
+    vim.api.nvim_buf_delete(w_input_buf.buf, { force = true })
+    -- The following is not needed, since the buffer is deleted above:
+    -- vim.api.nvim_win_close(w_input, false)
+    vim.api.nvim_win_close(w_list, false)
+    if stopinsert then vim.cmd.stopinsert() end
+    local inf = s_selection_info:get()
+    if not err and opts.on_finish then
+      -- If on_finish opens another picker, the closing of this one can happen
+      -- in _too_ quick succession, so put a small delay in there.
+      --
+      -- TODO: figure out _why_ this is actually happening, and then a better
+      -- way to handle this.
+      vim.defer_fn(function()
+        if esc then
+          opts.on_finish({}, {})
+        else
+          opts.on_finish(inf.items, inf.indices)
+        end
+      end, 100)
+    end
+  end
+
+  -- On selection info changed:
+  tracker.create_effect(
+    safe_wrap(function()
+      local inf = s_selection_info:get()
+      if opts.on_selection_changed then opts.on_selection_changed(inf.items, inf.indices) end
+    end),
+    'e:selection_changed'
+  )
+
+  --
+  -- Public API (i.e., `controller`):
+  -- We will fill in the methods further down, but we need this variable in scope so that it can be
+  -- closed over by some of the event handlers:
+  --
+  local controller = {}
+
+  --
+  -- Events
+  --
+  vim.keymap.set('i', '<Esc>', function() H.finish(true) end, { buffer = w_input_buf.buf })
+
+  vim.keymap.set('i', '<CR>', function() H.finish() end, { buffer = w_input_buf.buf })
+
+  local function action_next_line()
+    local max_line = #s_filtered_items:get()
+    local next_cursor_index = clamp(1, s_cursor_index:get() + 1, max_line)
+    if next_cursor_index - s_top_offset:get() > s_w_list_coords:get().height then
+      s_top_offset:set(s_top_offset:get() + 1)
+    end
+    s_cursor_index:set(next_cursor_index)
+  end
+  vim.keymap.set('i', '<C-n>', safe_wrap(action_next_line), { buffer = w_input_buf.buf, desc = 'Picker: next' })
+
+  vim.keymap.set(
+    'i',
+    '<C-p>',
+    safe_wrap(function()
+      local max_line = #s_filtered_items:get()
+      local next_cursor_index = clamp(1, s_cursor_index:get() - 1, max_line)
+      if next_cursor_index - s_top_offset:get() < 1 then s_top_offset:set(s_top_offset:get() - 1) end
+      s_cursor_index:set(next_cursor_index)
+    end),
+    { buffer = w_input_buf.buf, desc = 'Picker: previous' }
+  )
+
+  vim.keymap.set(
+    'i',
+    '<Tab>',
+    safe_wrap(function()
+      if not opts.multi then return end
+
+      local index = s_filtered_items:get()[s_cursor_index:get()].orig_idx
+      if vim.tbl_contains(s_selected_indices:get(), index) then
+        s_selected_indices:set(vim.iter(s_selected_indices:get()):filter(function(i) return i ~= index end):totable())
+      else
+        local new_selected_indices = shallow_copy_arr(s_selected_indices:get())
+        table.insert(new_selected_indices, index)
+        s_selected_indices:set(new_selected_indices)
+      end
+      action_next_line()
+    end),
+    { buffer = w_input_buf.buf }
+  )
+
+  for key, fn in pairs(opts.mappings or {}) do
+    vim.keymap.set('i', key, safe_wrap(function() return fn(controller) end), { buffer = w_input_buf.buf })
+  end
+
+  -- Render:
+  H.unsubscribe_render_effect = tracker.create_effect(
+    safe_wrap(function()
+      local selected_indices = s_selected_indices:get()
+      local top_offset = s_top_offset:get()
+      local cursor_index = s_cursor_index:get()
+      --- @type { filtered_idx: number; orig_idx: number; item: T; formatted: string }[]
+      local visible_items = s_visible_items:get()
+
+      -- The above has to run in the execution context for the signaling to work, but
+      -- the following cannot run in a NeoVim loop-callback:
+      vim.schedule(function()
+        w_list_buf:render(TreeBuilder.new()
+          :nest(function(tb)
+            for loop_idx, inf in ipairs(visible_items) do
+              local is_cur_line = inf.filtered_idx == cursor_index
+              local is_selected = vim.tbl_contains(selected_indices, inf.orig_idx)
+
+              tb:put(loop_idx > 1 and '\n')
+              tb:put(is_cur_line and h('text', { hl = 'Structure' }, '❯') or ' ')
+              tb:put(is_selected and h('text', { hl = 'Comment' }, '* ') or '  ')
+              tb:put(inf.formatted)
+            end
+          end)
+          :tree())
+
+        -- set the window viewport to have the first line in view:
+        pcall(vim.api.nvim_win_call, w_list, function() vim.fn.winrestview { topline = 1 } end)
+        pcall(vim.api.nvim_win_set_cursor, w_list, { cursor_index - top_offset, 0 })
+      end)
+    end),
+    'e:render'
+  )
+
+  --
+  -- Populate the public API:
+  --
+  function controller.get_items()
+    return safe_run(function() return s_items_raw:get() end)
+  end
+
+  ---@param items T[]
+  function controller.set_items(items)
+    return safe_run(function() s_items_raw:set(items) end)
+  end
+
+  function controller.set_filter_text(filter_text)
+    return safe_run(function()
+      vim.api.nvim_win_call(w_input, function() vim.api.nvim_set_current_line(filter_text) end)
+    end)
+  end
+
+  function controller.get_selected_indices()
+    return safe_run(function() return s_selection_info:get().indices end)
+  end
+
+  function controller.get_selected_items()
+    return safe_run(function() return s_selection_info:get().items end)
+  end
+
+  --- @param indicies number[]
+  ---@param ephemeral? boolean
+  function controller.set_selected_indices(indicies, ephemeral)
+    return safe_run(function()
+      if ephemeral == nil then ephemeral = false end
+
+      if ephemeral and #indicies == 1 then
+        local matching_filtered_item_idx, _ = vim
+          .iter(s_filtered_items:get())
+          :enumerate()
+          :find(function(_idx, inf) return inf.orig_idx == indicies[1] end)
+        if matching_filtered_item_idx ~= nil then s_cursor_index:set(indicies[1]) end
+      else
+        if not opts.multi then
+          local err = 'Cannot set multiple selected indices on a single-select picker'
+          H.finish(true, err)
+          error(err)
+        end
+        s_selected_indices:set(indicies)
+      end
+    end)
+  end
+
+  function controller.close()
+    return safe_run(function() H.finish(true) end)
+  end
+
+  return controller --[[@as SelectController]]
+end
+
+--------------------------------------------------------------------------------
+-- END create_picker
+--------------------------------------------------------------------------------
+
+--------------------------------------------------------------------------------
+-- vim.ui.select override
+--------------------------------------------------------------------------------
+
+local ORIGINAL_UI_SELECT
+function M.register_ui_select()
+  ORIGINAL_UI_SELECT = vim.ui.select
+  --- @generic T
+  --- @param items `T`[]
+  --- @param opts { prompt?: string, kind?: any, format_item?: fun(item: T):string }
+  --- @param cb fun(item: T|nil):any
+  function vim.ui.select(items, opts, cb)
+    M.create_picker {
+      items = items,
+      format_item = function(item)
+        local s = opts.format_item and opts.format_item(item) or tostring(item)
+        s = s:gsub('<', '&lt;')
+        return s
+      end,
+      on_finish = function(sel_items)
+        if #sel_items == 0 then cb(nil) end
+        cb(sel_items[#sel_items])
+      end,
+    }
+  end
+end
+function M.unregister_ui_select() vim.ui.select = ORIGINAL_UI_SELECT end
+
+--------------------------------------------------------------------------------
+-- Built-in pickers
+-- 1. files
+-- 2. buffers
+-- 3. code-symbols
+--------------------------------------------------------------------------------
+
+--- @param opts? { limit?: number }
+function M.files(opts)
+  opts = opts or {}
+  opts.limit = opts.limit or 10000
+
+  local cmd = {}
+  if vim.fn.executable 'rg' then
+    cmd = {
+      'rg',
+      '--color=never',
+      '--files',
+      '--hidden',
+      '--follow',
+      '-g',
+      '!.git',
+      '-g',
+      '!node_modules',
+      '-g',
+      '!target',
+    }
+  elseif vim.fn.executable 'fd' then
+    cmd = {
+      'fd',
+      '--color=never',
+      '--type',
+      'f',
+      '--hidden',
+      '--follow',
+      '--exclude',
+      '.git',
+      '--exclude',
+      'node_modules',
+      '--exclude',
+      'target',
+    }
+  elseif vim.fn.executable 'find' then
+    cmd = {
+      'find',
+      '-type',
+      'f',
+      '-not',
+      '-path',
+      "'*/.git/*'",
+      '-not',
+      '-path',
+      "'*/node_modules/*'",
+      '-not',
+      '-path',
+      "'*/target/*'",
+      '-printf',
+      "'%P\n'",
+    }
+  end
+
+  if #cmd == 0 then
+    vim.notify('rg/fd/find executable not found: cannot list files', vim.log.levels.ERROR)
+    return
+  end
+
+  -- Keep track of the job that will list files independent from the picker. We
+  -- will stream lines from this process to the picker as they come in:
+  local job_inf = { id = 0, proc_lines = {}, notified_over_limit = false }
+
+  -- Initially, create the picker with no items:
+  local picker = M.create_picker {
+    multi = true,
+    items = {},
+
+    --- @params items string[]
+    on_finish = function(items)
+      pcall(vim.fn.jobstop, job_inf.id)
+
+      if #items == 0 then return end
+      if #items == 1 then
+        vim.cmd.edit(items[1])
+      else
+        -- populate quickfix:
+        vim.fn.setqflist(vim
+          .iter(items)
+          :map(
+            function(item)
+              return {
+                filename = item,
+                lnum = 1,
+                col = 1,
+              }
+            end
+          )
+          :totable())
+        vim.cmd.copen()
+      end
+    end,
+
+    mappings = {
+      ['<C-t>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in new tab:
+        for _, item in ipairs(items) do
+          vim.cmd.tabnew(item)
+        end
+      end,
+
+      ['<C-v>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in vertical split:
+        for _, item in ipairs(items) do
+          vim.cmd.vsplit(item)
+        end
+      end,
+
+      ['<C-s>'] = function(sel)
+        sel.close()
+        --- @type string[]
+        local items = sel.get_selected_items()
+
+        -- open in horizontal split:
+        for _, item in ipairs(items) do
+          vim.cmd.split(item)
+        end
+      end,
+    },
+  }
+
+  -- Kick off the process that lists the files. As lines come in, send them to
+  -- the picker:
+  job_inf.id = vim.fn.jobstart(cmd, {
+    --- @param data string[]
+    on_stdout = vim.schedule_wrap(function(_chanid, data, _name)
+      local lines = job_inf.proc_lines
+      local function set_lines_as_items_state()
+        picker.set_items(vim
+          .iter(lines)
+          :enumerate()
+          :filter(function(idx, item)
+            -- Filter out an incomplete last line:
+            local is_last_line = idx == #lines
+            if is_last_line and item == '' then return false end
+            return true
+          end)
+          :map(function(_, item) return item end)
+          :totable())
+      end
+
+      -- It's just not a good idea to process large lists with Lua. The default
+      -- limit is 10,000 items, and even crunching through this is iffy on a
+      -- fast laptop. Show a warning and truncate the list in this case.
+      if #lines >= opts.limit then
+        if not job_inf.notified_over_limit then
+          vim.notify('Picker list is too large (truncating list to ' .. opts.limit .. ' items)', vim.log.levels.WARN)
+          job_inf.notified_over_limit = true
+        end
+        return
+      end
+
+      -- :help channel-lines
+
+      local eof = #data == 1 and data[1] == ''
+      if eof then set_lines_as_items_state() end
+
+      -- Complete the previous line:
+      if #lines > 0 then lines[#lines] = lines[#lines] .. table.remove(data, 1) end
+
+      for _, l in ipairs(data) do
+        table.insert(lines, l)
+      end
+
+      set_lines_as_items_state()
+    end),
+  })
+end
+
+function M.buffers()
+  local cwd = vim.fn.getcwd(0, 0)
+  -- ensure that `cwd` ends with a trailing slash:
+  if cwd[#cwd] ~= '/' then cwd = cwd .. '/' end
+
+  --- @type { name: string; changed: number; bufnr: number }[]
+  local bufs = vim.fn.getbufinfo { buflisted = 1 }
+
+  M.create_picker {
+    multi = true,
+    items = bufs,
+
+    --- @param item { name: string; changed: number; bufnr: number }
+    format_item = function(item)
+      local item_name = item.name
+      if item_name == '' then item_name = '[No Name]' end
+      -- trim leading `cwd` from the buffer name:
+      if item_name:sub(1, #cwd) == cwd then item_name = item_name:sub(#cwd + 1) end
+
+      return TreeBuilder.new()
+        :put(item.changed == 1 and '[+] ' or '    ')
+        :put(item_name)
+        :tree()
+    end,
+
+    --- @params items { bufnr: number }[]
+    on_finish = function(items)
+      if #items == 0 then return end
+      if #items == 1 then
+        vim.cmd.buffer(items[1].bufnr)
+      else
+        -- populate quickfix:
+        vim.fn.setqflist(vim
+          .iter(items)
+          :map(
+            function(item)
+              return {
+                bufnr = item.bufnr,
+                filename = item.name,
+                lnum = 1,
+                col = 1,
+              }
+            end
+          )
+          :totable())
+        vim.cmd.copen()
+      end
+    end,
+
+    mappings = {
+      ['<C-t>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in new tab:
+        for _, item in ipairs(items) do
+          vim.cmd.tabnew()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-v>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in new vertial split:
+        for _, item in ipairs(items) do
+          vim.cmd.vsplit()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-s>'] = function(sel)
+        sel.close()
+        --- @type { bufnr: number }[]
+        local items = sel.get_selected_items()
+
+        -- open in horizontal split:
+        for _, item in ipairs(items) do
+          vim.cmd.split()
+          vim.cmd.buffer(item.bufnr)
+        end
+      end,
+
+      ['<C-x>'] = function(sel)
+        local selected_items = sel.get_selected_items()
+        for _, item in ipairs(selected_items) do
+          -- delete the buffer
+          vim.cmd.bdelete(item.bufnr)
+        end
+
+        sel.set_selected_indices {}
+        sel.set_items(
+          vim
+            .iter(sel.get_items())
+            :filter(function(item) return not vim.tbl_contains(selected_items, item) end)
+            :totable()
+        )
+      end,
+    },
+  }
+end
+
+local IS_CODE_SYMBOL_RUNNING = false
+function M.lsp_code_symbols()
+  if IS_CODE_SYMBOL_RUNNING then return end
+  IS_CODE_SYMBOL_RUNNING = true
+
+  -- Avoid callback-hell with a wizard-based "steps"-system. Define each "step"
+  -- sequentially in the code, and wire up the callbacks to call the next step:
+  -- a simple, yet powerful, and easy to understand pattern/approach.
+  local STEPS = {}
+
+  --- @param info vim.lsp.LocationOpts.OnList
+  function STEPS._1_on_symbols(info)
+    M.create_picker {
+      items = info.items,
+      --- @param item { text: string }
+      format_item = function(item)
+        local s = item.text:gsub('<', '&lt;')
+        return s
+      end,
+      on_finish = STEPS._2_on_symbol_picked,
+    }
+  end
+
+  --- @param items { filename: string, lnum: integer, col: integer }[]
+  function STEPS._2_on_symbol_picked(items)
+    if #items == 0 then return STEPS._finally() end
+
+    local item = items[1]
+
+    -- Jump to the file/buffer:
+    local buf = vim.iter(vim.fn.getbufinfo { buflisted = 1 }):find(function(b) return b.name == item.filename end)
+    if buf ~= nil then
+      vim.api.nvim_win_set_buf(0, buf.bufnr)
+    else
+      vim.cmd.edit(item.filename)
+    end
+
+    -- Jump to the specific location:
+    vim.api.nvim_win_set_cursor(0, { item.lnum, item.col - 1 })
+    vim.cmd.normal 'zz'
+
+    STEPS._finally()
+  end
+
+  function STEPS._finally() IS_CODE_SYMBOL_RUNNING = false end
+
+  -- Kick off the async operation:
+  vim.lsp.buf.document_symbol { on_list = STEPS._1_on_symbols }
+end
+
+function M.setup()
+  utils.ucmd('Files', M.files)
+  utils.ucmd('Buffers', M.buffers)
+  utils.ucmd('Lspcodesymbols', M.lsp_code_symbols)
+  M.register_ui_select()
+end
+
+return M

examples/splitjoin.lua

@@ -1,38 +1,15 @@
---
+local vim_repeat = require 'u.repeat'
--- Split/Join: toggles between single-line and multi-line forms for bracketed expressions.
+local CodeWriter = require 'u.codewriter'
--- Example: { a, b, c } <-> {\n  a,\n  b,\n  c\n}
+local Range = require 'u.range'
--- Maps to gS in normal mode.
---
-local Range = require('u').Range
-local vim_repeat = require('u').repeat_
 
 local M = {}
 
---- @param bracket_range u.Range
+---@param bracket_range Range
---- @param left string
+---@param left string
---- @param right string
+---@param right string
 local function split(bracket_range, left, right)
-  local bufnr = bracket_range.start.bufnr
+  local code = CodeWriter.from_pos(bracket_range.start)
-  local first_line = Range.from_line(bufnr, bracket_range.start.lnum):text()
+  code:write_raw(left)
-  local ws = first_line:match '^%s*'
-  local expandtab = vim.bo[bufnr].expandtab
-  local shiftwidth = vim.bo[bufnr].shiftwidth
-
-  local indent_str, base_indent
-  if expandtab then
-    indent_str = string.rep(' ', shiftwidth)
-    base_indent = math.floor(#ws / shiftwidth)
-  else
-    indent_str = '\t'
-    base_indent = #ws
-  end
-
-  local lines = {}
-  local function write(line, indent_offset)
-    table.insert(lines, indent_str:rep(base_indent + (indent_offset or 0)) .. line)
-  end
-
-  table.insert(lines, left)
 
   local curr = bracket_range.start:next()
   if curr == nil then return end
@@ -50,7 +27,7 @@ local function split(bracket_range, left, right)
       if vim.tbl_contains({ ',', ';' }, curr:char()) then
         -- accumulate item:
         local item = vim.trim(Range.new(last_start, curr):text())
-        if item ~= '' then write(item, 1) end
+        if item ~= '' then code:indent():write(item) end
 
         local next_last_start = curr:next()
         if next_last_start == nil then break end
@@ -68,28 +45,24 @@ local function split(bracket_range, left, right)
   local pos_before_right = bracket_range.stop:must_next(-1)
   if last_start < pos_before_right then
     local item = vim.trim(Range.new(last_start, pos_before_right):text())
-    if item ~= '' then write(item, 1) end
+    if item ~= '' then code:indent():write(item) end
   end
 
-  write(right)
+  code:write(right)
-  bracket_range:replace(lines)
+  bracket_range:replace(code.lines)
 end
 
---- @param bracket_range u.Range
+---@param bracket_range Range
---- @param left string
+---@param left string
---- @param right string
+---@param right string
 local function join(bracket_range, left, right)
-  local inner_range = bracket_range:shrink(1)
+  local inner_range = Range.new(bracket_range.start:must_next(), bracket_range.stop:must_next(-1), bracket_range.mode)
-  if inner_range then
   local newline = vim
     .iter(inner_range:lines())
     :map(function(l) return vim.trim(l) end)
     :filter(function(l) return l ~= '' end)
     :join ' '
   bracket_range:replace { left .. newline .. right }
-  else
-    bracket_range:replace { left .. right }
-  end
 end
 
 local function splitjoin()
@@ -107,7 +80,7 @@ local function splitjoin()
 end
 
 function M.setup()
-  vim.keymap.set('n', 'gS', function() vim_repeat.run_repeatable(splitjoin) end)
+  vim.keymap.set('n', 'gS', function() vim_repeat.run(splitjoin) end)
 end
 
 return M

examples/surround.lua

@@ -1,19 +1,12 @@
---
+local vim_repeat = require 'u.repeat'
--- Surround: add, change, and delete surrounding characters (quotes, brackets, HTML tags).
+local opkeymap = require 'u.opkeymap'
---
+local Pos = require 'u.pos'
--- Mappings:
+local Range = require 'u.range'
---   ys{motion}{char} - add surround (e.g., ysiw" surrounds word with quotes)
+local Buffer = require 'u.buffer'
---   cs{from}{to}     - change surround (e.g., cs"' changes " to ')
+local CodeWriter = require 'u.codewriter'
---   ds{char}         - delete surround (e.g., ds" removes surrounding quotes)
---   S{char}          - surround visual selection
---
-local Range = require('u').Range
-local vim_repeat = require('u').repeat_
 
 local M = {}
 
-local ESC = vim.api.nvim_replace_termcodes('<Esc>', true, false, true)
-
 local surrounds = {
   [')'] = { left = '(', right = ')' },
   ['('] = { left = '( ', right = ' )' },
@@ -28,37 +21,36 @@ local surrounds = {
   ['`'] = { left = '`', right = '`' },
 }
 
---- @type { left: string, right: string } | nil
+---@return { left: string; right: string }|nil
-local CACHED_BOUNDS = nil
-
---- @return { left: string, right: string }|nil
 local function prompt_for_bounds()
-  if vim_repeat.is_repeating() then return CACHED_BOUNDS end
-
   local cn = vim.fn.getchar()
+  -- Check for non-printable characters:
   if type(cn) ~= 'number' or cn < 32 or cn > 126 then return end
   local c = vim.fn.nr2char(cn)
 
   if c == '<' then
+    -- Surround with a tag:
     vim.keymap.set('c', '>', '><CR>')
     local tag = '<' .. vim.fn.input '<'
     if tag == '<' then return end
     vim.keymap.del('c', '>')
     local endtag = '</' .. tag:sub(2):match '[^ >]*' .. '>'
-    CACHED_BOUNDS = { left = tag, right = endtag }
+    -- selene: allow(global_usage)
-    return CACHED_BOUNDS
+    return { left = tag, right = endtag }
   else
-    CACHED_BOUNDS = surrounds[c] or { left = c, right = c }
+    -- Default surround:
-    return CACHED_BOUNDS
+    return (surrounds)[c] or { left = c, right = c }
   end
 end
 
---- @param range u.Range
+---@param range Range
---- @param bounds { left: string, right: string }
+---@param bounds { left: string; right: string }
 local function do_surround(range, bounds)
   local left = bounds.left
   local right = bounds.right
   if range.mode == 'V' then
+    -- If we are surrounding multiple lines, we don't care about
+    -- space-padding:
     left = vim.trim(left)
     right = vim.trim(right)
   end
@@ -66,85 +58,59 @@ local function do_surround(range, bounds)
   if range.mode == 'v' then
     range:replace(left .. range:text() .. right)
   elseif range.mode == 'V' then
-    local bufnr = vim.api.nvim_get_current_buf()
+    local buf = Buffer.current()
-    local first_line = Range.from_line(bufnr, range.start.lnum):text()
+    local cw = CodeWriter.from_line(buf:line0(range.start.lnum):text(), buf.buf)
-    local ws = first_line:match '^%s*'
-    local expandtab = vim.bo[bufnr].expandtab
-    local shiftwidth = vim.bo[bufnr].shiftwidth
 
-    local indent_str, base_indent
+    -- write the left bound at the current indent level:
-    if expandtab then
+    cw:write(left)
-      indent_str = string.rep(' ', shiftwidth)
-      base_indent = math.floor(#ws / shiftwidth)
-    else
-      indent_str = '\t'
-      base_indent = #ws
-    end
 
-    local lines = {}
+    local curr_ident_prefix = cw.indent_str:rep(cw.indent_level)
-    local function write(line, indent_offset)
+    cw:indent(function(cw2)
-      table.insert(lines, indent_str:rep(base_indent + (indent_offset or 0)) .. line)
-    end
-
-    write(left)
-    local indent_prefix = indent_str:rep(base_indent)
       for _, line in ipairs(range:lines()) do
-      if line:sub(1, #indent_prefix) == indent_prefix then line = line:sub(#indent_prefix + 1) end
+        -- trim the current indent prefix from the line:
-      write(line, 1)
+        if line:sub(1, #curr_ident_prefix) == curr_ident_prefix then
+          --
+          line = line:sub(#curr_ident_prefix + 1)
         end
-    write(right)
 
-    range:replace(lines)
+        cw2:write(line)
+      end
+    end)
+
+    -- write the right bound at the current indent level:
+    cw:write(right)
+
+    range:replace(cw.lines)
   end
 
   range.start:save_to_pos '.'
 end
 
--- Add surround:
---- @param ty 'line' | 'char' | 'block'
-function _G.MySurroundOpFunc(ty)
-  if ty == 'block' then
-    -- We won't handle block-selection:
-    return
-  end
-
-  local range = Range.from_op_func(ty)
-  local hl
-  if not vim_repeat.is_repeating() then hl = range:highlight('IncSearch', { priority = 999 }) end
-
-  local bounds = prompt_for_bounds()
-  if hl then hl.clear() end
-  if bounds == nil then return end
-
-  do_surround(range, bounds)
-end
-
 function M.setup()
   require('u.repeat').setup()
 
   -- Visual
-  vim.keymap.set('x', 'S', function()
+  vim.keymap.set('v', 'S', function()
+    local c = vim.fn.getcharstr()
     local range = Range.from_vtext()
-    local bounds = prompt_for_bounds()
+    local bounds = surrounds[c] or { left = c, right = c }
-    if bounds == nil then return end
+    vim_repeat.run(function()
-
       do_surround(range, bounds)
       -- this is a visual mapping: end in normal mode:
-    vim.cmd.normal(ESC)
+      vim.cmd { cmd = 'normal', args = { '' }, bang = true }
+    end)
   end, { noremap = true, silent = true })
 
   -- Change
   vim.keymap.set('n', 'cs', function()
-    local from_cn = vim.fn.getchar() --[[@as number]]
+    local from_cn = vim.fn.getchar()
     -- Check for non-printable characters:
     if from_cn < 32 or from_cn > 126 then return end
-
-    vim_repeat.run_repeatable(function()
     local from_c = vim.fn.nr2char(from_cn)
     local from = surrounds[from_c] or { left = from_c, right = from_c }
     local function get_fresh_arange()
-        local arange = Range.from_motion('a' .. from_c, { user_defined = true })
+      local arange = Range.from_text_object('a' .. from_c, { user_defined = true })
-        if arange == nil then return end
+      if arange == nil then return nil end
       if from_c == 'q' then
         from.left = arange.start:char()
         from.right = arange.stop:char()
@@ -153,12 +119,10 @@ function M.setup()
     end
 
     local arange = get_fresh_arange()
-      if arange == nil then return end
+    if arange == nil then return nil end
 
-      local hl_info1 = vim_repeat.is_repeating() and nil
+    local hl_info1 = Range.new(arange.start, arange.start, 'v'):highlight('IncSearch', { priority = 999 })
-        or Range.new(arange.start, arange.start, 'v'):highlight('IncSearch', { priority = 999 })
+    local hl_info2 = Range.new(arange.stop, arange.stop, 'v'):highlight('IncSearch', { priority = 999 })
-      local hl_info2 = vim_repeat.is_repeating() and nil
-        or Range.new(arange.stop, arange.stop, 'v'):highlight('IncSearch', { priority = 999 })
     local hl_clear = function()
       if hl_info1 then hl_info1.clear() end
       if hl_info2 then hl_info2.clear() end
@@ -168,39 +132,51 @@ function M.setup()
     hl_clear()
     if to == nil then return end
 
+    vim_repeat.run(function()
+      -- Re-fetch the arange, just in case this action is being repeated:
+      arange = get_fresh_arange()
+      if arange == nil then return nil end
+
       if from_c == 't' then
         -- For tags, we want to replace the inner text, not the tag:
-        local irange = Range.from_motion('i' .. from_c, { user_defined = true })
+        local irange = Range.from_text_object('i' .. from_c, { user_defined = true })
-        if arange == nil or irange == nil then return end
+        if arange == nil or irange == nil then return nil end
 
-        local lrange, rrange = arange:difference(irange)
+        local lrange = Range.new(arange.start, irange.start:must_next(-1))
-        if not lrange or not rrange then return end
+        local rrange = Range.new(irange.stop:must_next(1), arange.stop)
 
         rrange:replace(to.right)
         lrange:replace(to.left)
       else
         -- replace `from.right` with `to.right`:
-        local right_text = arange:sub(-1, -#from.right)
+        local last_line = arange:line0(-1).text() --[[@as string]]
-        right_text:replace(to.right)
+        local from_right_match = last_line:match(vim.pesc(from.right) .. '$')
+        if from_right_match then
+          local match_start = arange.stop:clone()
+          match_start.col = match_start.col - #from_right_match + 1
+          Range.new(match_start, arange.stop):replace(to.right)
+        end
 
         -- replace `from.left` with `to.left`:
-        local left_text = arange:sub(1, #from.left)
+        local first_line = arange:line0(0).text() --[[@as string]]
-        left_text:replace(to.left)
+        local from_left_match = first_line:match('^' .. vim.pesc(from.left))
+        if from_left_match then
+          local match_end = arange.start:clone()
+          match_end.col = match_end.col + #from_left_match - 1
+          Range.new(arange.start, match_end):replace(to.left)
+        end
       end
     end)
   end, { noremap = true, silent = true })
 
   -- Delete
-  local CACHED_DELETE_FROM = nil
   vim.keymap.set('n', 'ds', function()
-    vim_repeat.run_repeatable(function()
+    local txt_obj = vim.fn.getcharstr()
-      local txt_obj = vim_repeat.is_repeating() and CACHED_DELETE_FROM or vim.fn.getcharstr()
+    vim_repeat.run(function()
-      CACHED_DELETE_FROM = txt_obj
+      local buf = Buffer.current()
-
+      local irange = Range.from_text_object('i' .. txt_obj)
-      local bufnr = vim.api.nvim_get_current_buf()
+      local arange = Range.from_text_object('a' .. txt_obj)
-      local irange = Range.from_motion('i' .. txt_obj)
+      if arange == nil or irange == nil then return nil end
-      local arange = Range.from_motion('a' .. txt_obj)
-      if arange == nil or irange == nil then return end
       local starting_cursor_pos = arange.start:clone()
 
       -- Now, replace `arange` with the content of `irange`.  If `arange` was multiple lines,
@@ -211,19 +187,28 @@ function M.setup()
         -- Dedenting moves the cursor, so we need to set the cursor to a consistent starting spot:
         arange.start:save_to_pos '.'
         -- Dedenting also changed the inner text, so re-acquire it:
-        arange = Range.from_motion('a' .. txt_obj)
+        arange = Range.from_text_object('a' .. txt_obj)
-        irange = Range.from_motion('i' .. txt_obj)
+        irange = Range.from_text_object('i' .. txt_obj)
         if arange == nil or irange == nil then return end -- should never be true
         arange:replace(irange:lines())
-        -- `arange:replace(..)` updates its own `stop` position, so we will use
+
-        -- `arange` as the final resulting range that holds the modified text
+        local final_range = Range.new(
+          arange.start,
+          Pos.new(
+            arange.stop.buf,
+            irange.start.lnum + (arange.stop.lnum + arange.start.lnum),
+            arange.stop.col,
+            arange.stop.off
+          ),
+          irange.mode
+        )
 
         -- delete last line, if it is empty:
-        local last = Range.from_line(bufnr, arange.stop.lnum)
+        local last = buf:line0(final_range.stop.lnum)
         if last:text():match '^%s*$' then last:replace(nil) end
 
         -- delete first line, if it is empty:
-        local first = Range.from_line(bufnr, arange.start.lnum)
+        local first = buf:line0(final_range.start.lnum)
         if first:text():match '^%s*$' then first:replace(nil) end
       else
         -- trim start:
@@ -235,10 +220,35 @@ function M.setup()
     end)
   end, { noremap = true, silent = true })
 
-  vim.keymap.set('n', 'ys', function()
+  opkeymap('n', 'ys', function(range)
-    vim.o.operatorfunc = 'v:lua.MySurroundOpFunc'
+    local hl_info = range:highlight('IncSearch', { priority = 999 })
-    return 'g@'
+
-  end, { expr = true })
+    ---@type { left: string; right: string }
+    local bounds
+    -- selene: allow(global_usage)
+    if _G.my_surround_bounds ~= nil then
+      -- This command was repeated with `.`, we don't need
+      -- to prompt for the bounds:
+      -- selene: allow(global_usage)
+      bounds = _G.my_surround_bounds
+    else
+      local prompted_bounds = prompt_for_bounds()
+      if prompted_bounds == nil and hl_info then return hl_info.clear() end
+      if prompted_bounds then bounds = prompted_bounds end
+    end
+
+    if hl_info then hl_info.clear() end
+    do_surround(range, bounds)
+    -- selene: allow(global_usage)
+    _G.my_surround_bounds = nil
+
+    -- return repeatable injection
+    return function()
+      -- on_repeat, we "stage" the bounds that we were originally called with:
+      -- selene: allow(global_usage)
+      _G.my_surround_bounds = bounds
+    end
+  end)
 end
 
 return M

examples/text-objects.lua

@@ -1,47 +1,58 @@
---
+local utils = require 'u.utils'
--- Custom text objects:
+local Pos = require 'u.pos'
---   ag   - whole file
+local Range = require 'u.range'
---   a.   - current line
+local Buffer = require 'u.buffer'
---   aq/iq - nearest quote (any type)
---   a"/i", a'/i', a`/i` - specific quotes
---   al"/il", al'/il', al`/il` - "last" quote (searches backward)
---   alB/ilB, al]/il], alb/ilb, al>/il> - "last" bracket objects
---
-local u = require 'u'
-local Pos = u.Pos
-local Range = u.Range
 
 local M = {}
 
 function M.setup()
   -- Select whole file:
-  u.define_txtobj('ag', function() return Range.from_buf_text(0) end)
+  utils.define_text_object('ag', function() return Buffer.current():all() end)
 
   -- Select current line:
-  u.define_txtobj('a.', function() return Range.from_line(0, Pos.from_pos('.').lnum) end)
+  utils.define_text_object('a.', function()
+    local lnum = Pos.from_pos('.').lnum
+    return Buffer.current():line0(lnum)
+  end)
 
   -- Select the nearest quote:
-  u.define_txtobj('aq', function() return Range.find_nearest_quotes() end)
+  utils.define_text_object('aq', function() return Range.find_nearest_quotes() end)
-  u.define_txtobj('iq', function()
+  utils.define_text_object('iq', function()
     local range = Range.find_nearest_quotes()
     if range == nil then return end
     return range:shrink(1)
   end)
 
   ---Selects the next quote object (searches forward)
-  --- @param q string
+  ---@param q string
   local function define_quote_obj(q)
-    local function select_around() return Range.from_motion('a' .. q) end
+    local function select_around()
+      -- Operator mappings are effectively running in visual mode, the way
+      -- `define_text_object` is implemented, so feed the keys `a${q}` to vim
+      -- to select the appropriate text-object
+      vim.cmd { cmd = 'normal', args = { 'a' .. q }, bang = true }
 
-    u.define_txtobj('a' .. q, function() return select_around() end)
+      -- Now check on the visually selected text:
-    u.define_txtobj('i' .. q, function()
+      local range = Range.from_vtext()
-      local range = select_around()
+      if range:is_empty() then return range.start end
-      if range == nil or range:is_empty() then return range end
+      range.start = range.start:find_next(1, q) or range.start
+      range.stop = range.stop:find_next(-1, q) or range.stop
+      return range
+    end
 
-      local start_next = range.start:next(1) or range.start
+    utils.define_text_object('a' .. q, function() return select_around() end)
-      local stop_prev = range.stop:next(-1)
+    utils.define_text_object('i' .. q, function()
-      if start_next > stop_prev then return Range.new(start_next) end
+      local range_or_pos = select_around()
-      return range:shrink(1) or range
+      if Range.is(range_or_pos) then
+        local start_next = range_or_pos.start:next(1)
+        local stop_prev = range_or_pos.stop:next(-1)
+        if start_next > stop_prev then return start_next end
+
+        local range = range_or_pos:shrink(1)
+        return range
+      else
+        return range_or_pos
+      end
     end)
   end
   define_quote_obj [["]]
@@ -49,26 +60,36 @@ function M.setup()
   define_quote_obj [[`]]
 
   ---Selects the "last" quote object (searches backward)
-  --- @param q string
+  ---@param q string
   local function define_last_quote_obj(q)
     local function select_around()
       local curr = Pos.from_pos('.'):find_next(-1, q)
       if not curr then return end
       -- Reset visual selection to current context:
-      curr:save_to_pos '.'
+      Range.new(curr, curr):set_visual_selection()
-      return Range.from_motion('a' .. q)
+      vim.cmd.normal('a' .. q)
+      local range = Range.from_vtext()
+      if range:is_empty() then return range.start end
+      range.start = range.start:find_next(1, q) or range.start
+      range.stop = range.stop:find_next(-1, q) or range.stop
+      return range
     end
 
-    u.define_txtobj('al' .. q, function() return select_around() end)
+    utils.define_text_object('al' .. q, function() return select_around() end)
-    u.define_txtobj('il' .. q, function()
+    utils.define_text_object('il' .. q, function()
-      local range = select_around()
+      local range_or_pos = select_around()
-      if range == nil or range:is_empty() then return range end
+      if range_or_pos == nil then return end
 
-      local start_next = range.start:next(1) or range.start
+      if Range.is(range_or_pos) then
-      local stop_prev = range.stop:next(-1)
+        local start_next = range_or_pos.start:next(1)
-      if start_next > stop_prev then return Range.new(start_next) end
+        local stop_prev = range_or_pos.stop:next(-1)
+        if start_next > stop_prev then return start_next end
 
-      return range:shrink(1) or range
+        local range = range_or_pos:shrink(1)
+        return range
+      else
+        return range_or_pos
+      end
     end)
   end
   define_last_quote_obj [["]]
@@ -90,8 +111,8 @@ function M.setup()
     local keybinds = { ... }
     table.insert(keybinds, b)
     for _, k in ipairs(keybinds) do
-      u.define_txtobj('al' .. k, function() return select_around() end)
+      utils.define_text_object('al' .. k, function() return select_around() end)
-      u.define_txtobj('il' .. k, function()
+      utils.define_text_object('il' .. k, function()
         local range = select_around()
         return range and range:shrink(1)
       end)

lua/u/buffer.lua

@@ -0,0 +1,86 @@
+local Range = require 'u.range'
+local Renderer = require 'u.renderer'.Renderer
+
+---@class Buffer
+---@field buf number
+---@field private renderer Renderer
+local Buffer = {}
+
+---@param buf? number
+---@return Buffer
+function Buffer.from_nr(buf)
+  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
+
+  local renderer = Renderer.new(buf)
+  return setmetatable({
+    buf = buf,
+    renderer = renderer,
+  }, { __index = Buffer })
+end
+
+---@return Buffer
+function Buffer.current() return Buffer.from_nr(0) end
+
+---@param listed boolean
+---@param scratch boolean
+---@return Buffer
+function Buffer.create(listed, scratch) return Buffer.from_nr(vim.api.nvim_create_buf(listed, scratch)) end
+
+function Buffer:set_tmp_options()
+  self:set_option('bufhidden', 'delete')
+  self:set_option('buflisted', false)
+  self:set_option('buftype', 'nowrite')
+end
+
+---@param nm string
+function Buffer:get_option(nm) return vim.api.nvim_get_option_value(nm, { buf = self.buf }) end
+
+---@param nm string
+function Buffer:set_option(nm, val) return vim.api.nvim_set_option_value(nm, val, { buf = self.buf }) end
+
+---@param nm string
+function Buffer:get_var(nm) return vim.api.nvim_buf_get_var(self.buf, nm) end
+
+---@param nm string
+function Buffer:set_var(nm, val) return vim.api.nvim_buf_set_var(self.buf, nm, val) end
+
+function Buffer:line_count() return vim.api.nvim_buf_line_count(self.buf) end
+
+function Buffer:all() return Range.from_buf_text(self.buf) end
+
+function Buffer:is_empty() return self:line_count() == 1 and self:line0(0):text() == '' end
+
+---@param line string
+function Buffer:append_line(line)
+  local start = -1
+  if self:is_empty() then start = -2 end
+  vim.api.nvim_buf_set_lines(self.buf, start, -1, false, { line })
+end
+
+---@param num number 0-based line index
+function Buffer:line0(num)
+  if num < 0 then return self:line0(self:line_count() + num) end
+  return Range.from_line(self.buf, num)
+end
+
+---@param start number 0-based line index
+---@param stop number 0-based line index
+function Buffer:lines(start, stop) return Range.from_lines(self.buf, start, stop) end
+
+---@param txt_obj string
+---@param opts? { contains_cursor?: boolean; pos?: Pos }
+function Buffer:text_object(txt_obj, opts)
+  opts = vim.tbl_extend('force', opts or {}, { buf = self.buf })
+  return Range.from_text_object(txt_obj, opts)
+end
+
+--- @param event string|string[]
+--- @param opts vim.api.keyset.create_autocmd
+function Buffer:autocmd(event, opts)
+  vim.api.nvim_create_autocmd(event, vim.tbl_extend('force', opts, { buffer = self.buf }))
+end
+
+--- @param tree Tree
+function Buffer:render(tree) return self.renderer:render(tree) end
+
+return Buffer

lua/u/codewriter.lua

@@ -0,0 +1,76 @@
+local Buffer = require 'u.buffer'
+
+---@class CodeWriter
+---@field lines string[]
+---@field indent_level number
+---@field indent_str string
+local CodeWriter = {}
+
+---@param indent_level? number
+---@param indent_str? string
+---@return CodeWriter
+function CodeWriter.new(indent_level, indent_str)
+  if indent_level == nil then indent_level = 0 end
+  if indent_str == nil then indent_str = '  ' end
+
+  local cw = {
+    lines = {},
+    indent_level = indent_level,
+    indent_str = indent_str,
+  }
+  setmetatable(cw, { __index = CodeWriter })
+  return cw
+end
+
+---@param p Pos
+function CodeWriter.from_pos(p)
+  local line = Buffer.from_nr(p.buf):line0(p.lnum):text()
+  return CodeWriter.from_line(line, p.buf)
+end
+
+---@param line string
+---@param buf? number
+function CodeWriter.from_line(line, buf)
+  if buf == nil then buf = vim.api.nvim_get_current_buf() end
+
+  local ws = line:match '^%s*'
+  local expandtab = vim.api.nvim_get_option_value('expandtab', { buf = buf })
+  local shiftwidth = vim.api.nvim_get_option_value('shiftwidth', { buf = buf })
+
+  local indent_level = 0
+  local indent_str = ''
+  if expandtab then
+    while #indent_str < shiftwidth do
+      indent_str = indent_str .. ' '
+    end
+    indent_level = #ws / shiftwidth
+  else
+    indent_str = '\t'
+    indent_level = #ws
+  end
+
+  return CodeWriter.new(indent_level, indent_str)
+end
+
+---@param line string
+function CodeWriter:write_raw(line)
+  if line:find '\n' then error 'line contains newline character' end
+  table.insert(self.lines, line)
+end
+
+---@param line string
+function CodeWriter:write(line) self:write_raw(self.indent_str:rep(self.indent_level) .. line) end
+
+---@param f? fun(cw: CodeWriter):any
+function CodeWriter:indent(f)
+  local cw = {
+    lines = self.lines,
+    indent_level = self.indent_level + 1,
+    indent_str = self.indent_str,
+  }
+  setmetatable(cw, { __index = CodeWriter })
+  if f ~= nil then f(cw) end
+  return cw
+end
+
+return CodeWriter

lua/u/opkeymap.lua

@@ -0,0 +1,43 @@
+local Range = require 'u.range'
+local vim_repeat = require 'u.repeat'
+
+---@type fun(range: Range): nil|(fun():any)
+local __U__OpKeymapOpFunc_rhs = nil
+
+--- This is the global utility function used for operatorfunc
+--- in opkeymap
+---@type nil|fun(range: Range): fun():any|nil
+---@param ty 'line'|'char'|'block'
+-- selene: allow(unused_variable)
+function __U__OpKeymapOpFunc(ty)
+  if __U__OpKeymapOpFunc_rhs ~= nil then
+    local range = Range.from_op_func(ty)
+    local repeat_inject = __U__OpKeymapOpFunc_rhs(range)
+
+    vim_repeat.set(function()
+      vim.o.operatorfunc = 'v:lua.__U__OpKeymapOpFunc'
+      if repeat_inject ~= nil and type(repeat_inject) == 'function' then repeat_inject() end
+      vim_repeat.native_repeat()
+    end)
+  end
+end
+
+--- Registers a function that operates on a text-object, triggered by the given prefix (lhs).
+--- It works in the following way:
+--- 1. An expression-map is set, so that whatever the callback returns is executed by Vim (in this case `g@`)
+---    g@: tells vim to way for a motion, and then call operatorfunc.
+--- 2. The operatorfunc is set to a lua function that computes the range being operated over, that
+---    then calls the original passed callback with said range.
+---@param mode string|string[]
+---@param lhs string
+---@param rhs fun(range: Range): nil|(fun():any) This function may return another function, which is called whenever the operator is repeated
+---@param opts? vim.keymap.set.Opts
+local function opkeymap(mode, lhs, rhs, opts)
+  vim.keymap.set(mode, lhs, function()
+    __U__OpKeymapOpFunc_rhs = rhs
+    vim.o.operatorfunc = 'v:lua.__U__OpKeymapOpFunc'
+    return 'g@'
+  end, vim.tbl_extend('force', opts or {}, { expr = true }))
+end
+
+return opkeymap

lua/u/pos.lua

@@ -0,0 +1,239 @@
+local MAX_COL = vim.v.maxcol
+
+---@param buf number
+---@param lnum number
+local function line_text(buf, lnum) return vim.api.nvim_buf_get_lines(buf, lnum, lnum + 1, false)[1] end
+
+---@class Pos
+---@field buf number buffer number
+---@field lnum number 1-based line index
+---@field col number 1-based column index
+---@field off number
+local Pos = {}
+Pos.MAX_COL = MAX_COL
+
+---@param buf? number
+---@param lnum number
+---@param col number
+---@param off? number
+---@return Pos
+function Pos.new(buf, lnum, col, off)
+  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
+  if off == nil then off = 0 end
+  local pos = {
+    buf = buf,
+    lnum = lnum,
+    col = col,
+    off = off,
+  }
+
+  local function str()
+    if pos.off ~= 0 then
+      return string.format('Pos(%d:%d){buf=%d, off=%d}', pos.lnum, pos.col, pos.buf, pos.off)
+    else
+      return string.format('Pos(%d:%d){buf=%d}', pos.lnum, pos.col, pos.buf)
+    end
+  end
+  setmetatable(pos, {
+    __index = Pos,
+    __tostring = str,
+    __lt = Pos.__lt,
+    __le = Pos.__le,
+    __eq = Pos.__eq,
+  })
+  return pos
+end
+
+function Pos.is(x)
+  local mt = getmetatable(x)
+  return mt and mt.__index == Pos
+end
+
+function Pos.__lt(a, b) return a.lnum < b.lnum or (a.lnum == b.lnum and a.col < b.col) end
+function Pos.__le(a, b) return a < b or a == b end
+function Pos.__eq(a, b) return a.lnum == b.lnum and a.col == b.col end
+
+---@param name string
+---@return Pos
+function Pos.from_pos(name)
+  local p = vim.fn.getpos(name)
+  local col = p[3]
+  if col ~= MAX_COL then col = col - 1 end
+  return Pos.new(p[1], p[2] - 1, col, p[4])
+end
+
+function Pos:clone() return Pos.new(self.buf, self.lnum, self.col, self.off) end
+
+---@return boolean
+function Pos:is_col_max() return self.col == MAX_COL end
+
+---@return number[]
+function Pos:as_vim() return { self.buf, self.lnum, self.col, self.off } end
+
+--- Normalize the position to a real position (take into account vim.v.maxcol).
+function Pos:as_real()
+  local col = self.col
+  if self:is_col_max() then
+    -- We could use utilities in this file to get the given line, but
+    -- since this is a low-level function, we are going to optimize and
+    -- use the API directly:
+    col = #line_text(self.buf, self.lnum) - 1
+  end
+  return Pos.new(self.buf, self.lnum, col, self.off)
+end
+
+---@param pos string
+function Pos:save_to_pos(pos)
+  if pos == '.' then
+    vim.api.nvim_win_set_cursor(0, { self.lnum + 1, self.col })
+    return
+  end
+
+  local p = self:as_real()
+  vim.fn.setpos(pos, { p.buf, p.lnum + 1, p.col + 1, p.off })
+end
+
+---@param mark string
+function Pos:save_to_mark(mark)
+  local p = self:as_real()
+  vim.api.nvim_buf_set_mark(p.buf, mark, p.lnum + 1, p.col, {})
+end
+
+---@return string
+function Pos:char()
+  local line = line_text(self.buf, self.lnum)
+  if line == nil then return '' end
+  return line:sub(self.col + 1, self.col + 1)
+end
+
+---@param dir? -1|1
+---@param must? boolean
+---@return Pos|nil
+function Pos:next(dir, must)
+  if must == nil then must = false end
+
+  if dir == nil or dir == 1 then
+    -- Next:
+    local num_lines = vim.api.nvim_buf_line_count(self.buf)
+    local last_line = line_text(self.buf, num_lines - 1) -- buf:line0(-1)
+    if self.lnum == num_lines - 1 and self.col == (#last_line - 1) then
+      if must then error 'error in Pos:next(): Pos:next() returned nil' end
+      return nil
+    end
+
+    local col = self.col + 1
+    local line = self.lnum
+    local line_max_col = #line_text(self.buf, self.lnum) - 1
+    if col > line_max_col then
+      col = 0
+      line = line + 1
+    end
+    return Pos.new(self.buf, line, col, self.off)
+  else
+    -- Previous:
+    if self.col == 0 and self.lnum == 0 then
+      if must then error 'error in Pos:next(): Pos:next() returned nil' end
+      return nil
+    end
+
+    local col = self.col - 1
+    local line = self.lnum
+    local prev_line_max_col = #(line_text(self.buf, self.lnum - 1) or '') - 1
+    if col < 0 then
+      col = math.max(prev_line_max_col, 0)
+      line = line - 1
+    end
+    return Pos.new(self.buf, line, col, self.off)
+  end
+end
+
+---@param dir? -1|1
+function Pos:must_next(dir)
+  local next = self:next(dir, true)
+  if next == nil then error 'unreachable' end
+  return next
+end
+
+---@param dir -1|1
+---@param predicate fun(p: Pos): boolean
+---@param test_current? boolean
+function Pos:next_while(dir, predicate, test_current)
+  if test_current and not predicate(self) then return end
+  local curr = self
+  while true do
+    local next = curr:next(dir)
+    if next == nil or not predicate(next) then break end
+    curr = next
+  end
+  return curr
+end
+
+---@param dir -1|1
+---@param predicate string|fun(p: Pos): boolean
+function Pos:find_next(dir, predicate)
+  if type(predicate) == 'string' then
+    local s = predicate
+    predicate = function(p) return s == p:char() end
+  end
+
+  ---@type Pos|nil
+  local curr = self
+  while curr ~= nil do
+    if predicate(curr) then return curr end
+    curr = curr:next(dir)
+  end
+  return curr
+end
+
+--- Finds the matching bracket/paren for the current position.
+---@param max_chars? number|nil
+---@param invocations? Pos[]
+---@return Pos|nil
+function Pos:find_match(max_chars, invocations)
+  if invocations == nil then invocations = {} end
+  if vim.tbl_contains(invocations, function(p) return self == p end, { predicate = true }) then return nil end
+  table.insert(invocations, self)
+
+  local openers = { '{', '[', '(', '<' }
+  local closers = { '}', ']', ')', '>' }
+  local c = self:char()
+  local is_opener = vim.tbl_contains(openers, c)
+  local is_closer = vim.tbl_contains(closers, c)
+  if not is_opener and not is_closer then return nil end
+
+  local i, _ = vim.iter(is_opener and openers or closers):enumerate():find(function(_, c2) return c == c2 end)
+  local c_match = (is_opener and closers or openers)[i]
+
+  ---@type Pos|nil
+  local cur = self
+  ---@return Pos|nil
+  local function adv()
+    if cur == nil then return nil end
+
+    if max_chars ~= nil then
+      max_chars = max_chars - 1
+      if max_chars < 0 then return nil end
+    end
+
+    return cur:next(is_opener and 1 or -1)
+  end
+
+  -- scan until we find a match:
+  cur = adv()
+  while cur ~= nil and cur:char() ~= c_match do
+    cur = adv()
+    if cur == nil then break end
+
+    local c2 = cur:char()
+    if c2 == c_match then break end
+
+    if vim.tbl_contains(openers, c2) or vim.tbl_contains(closers, c2) then
+      cur = cur:find_match(max_chars, invocations)
+      cur = adv() -- move past the match
+    end
+  end
+
+  return cur
+end
+
+return Pos

lua/u/range.lua

@@ -0,0 +1,522 @@
+local Pos = require 'u.pos'
+local State = require 'u.state'
+
+local orig_on_yank = (vim.hl or vim.highlight).on_yank
+local on_yank_enabled = true;
+((vim.hl or vim.highlight) --[[@as any]]).on_yank = function(opts)
+  if not on_yank_enabled then return end
+  return orig_on_yank(opts)
+end
+
+---@class Range
+---@field start Pos
+---@field stop Pos|nil
+---@field mode 'v'|'V'
+local Range = {}
+
+---@param start Pos
+---@param stop Pos|nil
+---@param mode? 'v'|'V'
+---@return Range
+function Range.new(start, stop, mode)
+  if stop ~= nil and stop < start then
+    start, stop = stop, start
+  end
+
+  local r = { start = start, stop = stop, mode = mode or 'v' }
+  local function str()
+    ---@param p Pos
+    local function posstr(p)
+      if p == nil then
+        return 'nil'
+      elseif p.off ~= 0 then
+        return string.format('Pos(%d:%d){off=%d}', p.lnum, p.col, p.off)
+      else
+        return string.format('Pos(%d:%d)', p.lnum, p.col)
+      end
+    end
+
+    local _1 = posstr(r.start)
+    local _2 = posstr(r.stop)
+    return string.format('Range{buf=%d, mode=%s, start=%s, stop=%s}', r.start.buf, r.mode, _1, _2)
+  end
+  setmetatable(r, { __index = Range, __tostring = str })
+  return r
+end
+
+function Range.is(x)
+  local mt = getmetatable(x)
+  return mt and mt.__index == Range
+end
+
+---@param lpos string
+---@param rpos string
+---@return Range
+function Range.from_marks(lpos, rpos)
+  local start = Pos.from_pos(lpos)
+  local stop = Pos.from_pos(rpos)
+
+  ---@type 'v'|'V'
+  local mode
+  if stop:is_col_max() then
+    mode = 'V'
+  else
+    mode = 'v'
+  end
+
+  return Range.new(start, stop, mode)
+end
+
+---@param buf? number
+function Range.from_buf_text(buf)
+  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
+  local num_lines = vim.api.nvim_buf_line_count(buf)
+
+  local start = Pos.new(buf, 0, 0)
+  local stop = Pos.new(buf, num_lines - 1, Pos.MAX_COL)
+  return Range.new(start, stop, 'V')
+end
+
+---@param buf? number
+---@param line number 0-based line index
+function Range.from_line(buf, line) return Range.from_lines(buf, line, line) end
+
+---@param buf? number
+---@param start_line number 0-based line index
+---@param stop_line number 0-based line index
+function Range.from_lines(buf, start_line, stop_line)
+  if buf == nil or buf == 0 then buf = vim.api.nvim_get_current_buf() end
+  if stop_line < 0 then
+    local num_lines = vim.api.nvim_buf_line_count(buf)
+    stop_line = num_lines + stop_line
+  end
+  return Range.new(Pos.new(buf, start_line, 0), Pos.new(buf, stop_line, Pos.MAX_COL), 'V')
+end
+
+---@param text_obj string
+---@param opts? { buf?: number; contains_cursor?: boolean; pos?: Pos, user_defined?: boolean }
+---@return Range|nil
+function Range.from_text_object(text_obj, opts)
+  opts = opts or {}
+  if opts.buf == nil then opts.buf = vim.api.nvim_get_current_buf() end
+  if opts.contains_cursor == nil then opts.contains_cursor = false end
+  if opts.user_defined == nil then opts.user_defined = false end
+
+  ---@type "a" | "i"
+  local selection_type = text_obj:sub(1, 1)
+  local obj_type = text_obj:sub(#text_obj, #text_obj)
+  local is_quote = vim.tbl_contains({ "'", '"', '`' }, obj_type)
+  local cursor = Pos.from_pos '.'
+
+  -- Yank, then read '[ and '] to know the bounds:
+  ---@type { start: Pos; stop: Pos }
+  local positions
+  vim.api.nvim_buf_call(opts.buf, function()
+    positions = State.run(0, function(s)
+      s:track_winview()
+      s:track_register '"'
+      s:track_pos '.'
+      s:track_pos "'["
+      s:track_pos "']"
+
+      if opts.pos ~= nil then opts.pos:save_to_pos '.' end
+
+      local null_pos = Pos.new(0, 0, 0, 0)
+      null_pos:save_to_pos "'["
+      null_pos:save_to_pos "']"
+
+      local prev_on_yank_enabled = on_yank_enabled
+      on_yank_enabled = false
+      vim.cmd.normal {
+        cmd = 'normal',
+        bang = not opts.user_defined,
+        args = { '""y' .. text_obj },
+        mods = { silent = true },
+      }
+      on_yank_enabled = prev_on_yank_enabled
+
+      local start = Pos.from_pos "'["
+      local stop = Pos.from_pos "']"
+
+      if
+        -- I have no idea why, but when yanking `i"`, the stop-mark is
+        -- placed on the ending quote. For other text-objects, the stop-
+        -- mark is placed before the closing character.
+        (is_quote and selection_type == 'i' and stop:char() == obj_type)
+        -- *Sigh*, this also sometimes happens for `it` as well.
+        or (text_obj == 'it' and stop:char() == '<')
+      then
+        stop = stop:next(-1) or stop
+      end
+      return { start = start, stop = stop }
+    end)
+  end)
+  local start = positions.start
+  local stop = positions.stop
+  if start == stop and start.lnum == 0 and start.col == 0 and start.off == 0 then return nil end
+  if opts.contains_cursor and not Range.new(start, stop):contains(cursor) then return nil end
+
+  if is_quote and selection_type == 'a' then
+    start = start:find_next(1, obj_type) or start
+    stop = stop:find_next(-1, obj_type) or stop
+  end
+
+  return Range.new(start, stop)
+end
+
+--- Get range information from the currently selected visual text.
+--- Note: from within a command mapping or an opfunc, use other specialized
+--- utilities, such as:
+--- * Range.from_cmd_args
+--- * Range.from_op_func
+function Range.from_vtext()
+  local r = Range.from_marks('v', '.')
+  if vim.fn.mode() == 'V' then r = r:to_linewise() end
+  return r
+end
+
+--- Get range information from the current text range being operated on
+--- as defined by an operator-pending function. Infers line-wise vs. char-wise
+--- based on the type, as given by the operator-pending function.
+---@param type 'line'|'char'|'block'
+function Range.from_op_func(type)
+  if type == 'block' then error 'block motions not supported' end
+
+  local range = Range.from_marks("'[", "']")
+  if type == 'line' then range = range:to_linewise() end
+  return range
+end
+
+--- Get range information from command arguments.
+---@param args unknown
+---@return Range|nil
+function Range.from_cmd_args(args)
+  ---@type 'v'|'V'
+  local mode
+  ---@type nil|Pos
+  local start
+  local stop
+  if args.range == 0 then
+    return nil
+  else
+    start = Pos.from_pos "'<"
+    stop = Pos.from_pos "'>"
+    if stop:is_col_max() then
+      mode = 'V'
+    else
+      mode = 'v'
+    end
+  end
+  return Range.new(start, stop, mode)
+end
+
+---
+function Range.find_nearest_brackets()
+  local a = Range.from_text_object('a<', { contains_cursor = true })
+  local b = Range.from_text_object('a[', { contains_cursor = true })
+  local c = Range.from_text_object('a(', { contains_cursor = true })
+  local d = Range.from_text_object('a{', { contains_cursor = true })
+  return Range.smallest { a, b, c, d }
+end
+
+function Range.find_nearest_quotes()
+  local a = Range.from_text_object([[a']], { contains_cursor = true })
+  if a ~= nil and a:is_empty() then a = nil end
+  local b = Range.from_text_object([[a"]], { contains_cursor = true })
+  if b ~= nil and b:is_empty() then b = nil end
+  local c = Range.from_text_object([[a`]], { contains_cursor = true })
+  if c ~= nil and c:is_empty() then c = nil end
+  return Range.smallest { a, b, c }
+end
+
+---@param ranges (Range|nil)[]
+function Range.smallest(ranges)
+  ---@type Range[]
+  local new_ranges = {}
+  for _, r in pairs(ranges) do
+    if r ~= nil then table.insert(new_ranges, r) end
+  end
+  ranges = new_ranges
+  if #ranges == 0 then return nil end
+
+  -- find smallest match
+  local max_start = ranges[1].start
+  local min_stop = ranges[1].stop
+  local result = ranges[1]
+
+  for _, r in ipairs(ranges) do
+    local start, stop = r.start, r.stop
+    if start > max_start and stop < min_stop then
+      max_start = start
+      min_stop = stop
+      result = r
+    end
+  end
+
+  return result
+end
+
+function Range:clone() return Range.new(self.start:clone(), self.stop ~= nil and self.stop:clone() or nil, self.mode) end
+function Range:line_count()
+  if self:is_empty() then return 0 end
+  return self.stop.lnum - self.start.lnum + 1
+end
+
+function Range:to_linewise()
+  local r = self:clone()
+
+  r.mode = 'V'
+  r.start.col = 0
+  if r.stop ~= nil then r.stop.col = Pos.MAX_COL end
+
+  return r
+end
+
+function Range:is_empty() return self.stop == nil end
+
+function Range:trim_start()
+  if self:is_empty() then return end
+
+  local r = self:clone()
+  while r.start:char():match '%s' do
+    local next = r.start:next(1)
+    if next == nil then break end
+    r.start = next
+  end
+  return r
+end
+
+function Range:trim_stop()
+  if self:is_empty() then return end
+
+  local r = self:clone()
+  while r.stop:char():match '%s' do
+    local next = r.stop:next(-1)
+    if next == nil then break end
+    r.stop = next
+  end
+  return r
+end
+
+---@param p Pos
+function Range:contains(p) return not self:is_empty() and p >= self.start and p <= self.stop end
+
+---@return string[]
+function Range:lines()
+  if self:is_empty() then return {} end
+
+  local lines = {}
+  for i = 0, self.stop.lnum - self.start.lnum do
+    local line = self:line0(i)
+    if line ~= nil then table.insert(lines, line.text()) end
+  end
+  return lines
+end
+
+---@return string
+function Range:text() return vim.fn.join(self:lines(), '\n') end
+
+---@param i number 1-based
+---@param j? number 1-based
+function Range:sub(i, j) return self:text():sub(i, j) end
+
+---@param l number
+---@return { line: string; idx0: { start: number; stop: number; }; lnum: number; range: fun():Range; text: fun():string }|nil
+function Range:line0(l)
+  if l < 0 then return self:line0(self:line_count() + l) end
+  if l > self:line_count() then return end
+
+  local line = vim.api.nvim_buf_get_lines(self.start.buf, self.start.lnum + l, self.start.lnum + l + 1, false)[1]
+  if line == nil then return end
+
+  local start = 0
+  local stop = #line - 1
+  if l == 0 then start = self.start.col end
+  if l == self.stop.lnum - self.start.lnum then stop = self.stop.col end
+  if stop == Pos.MAX_COL then stop = #line - 1 end
+  local lnum = self.start.lnum + l
+
+  return {
+    line = line,
+    idx0 = { start = start, stop = stop },
+    lnum = lnum,
+    range = function()
+      return Range.new(
+        Pos.new(self.start.buf, lnum, start, self.start.off),
+        Pos.new(self.start.buf, lnum, stop, self.stop.off),
+        'v'
+      )
+    end,
+    text = function() return line:sub(start + 1, stop + 1) end,
+  }
+end
+
+---@param replacement nil|string|string[]
+function Range:replace(replacement)
+  if replacement == nil then replacement = {} end
+  if type(replacement) == 'string' then replacement = vim.fn.split(replacement, '\n') end
+
+  local buf = self.start.buf
+  -- convert to start-inclusive, stop-exclusive coordinates:
+  local start_lnum, stop_lnum = self.start.lnum, (self.stop and self.stop.lnum or self.start.lnum) + 1
+  local start_col, stop_col = self.start.col, (self.stop and self.stop.col or self.start.col) + 1
+
+  local replace_type = (self:is_empty() and 'insert') or (self.mode == 'v' and 'region') or 'lines'
+
+  ---@param alnum number
+  ---@param acol number
+  ---@param blnum number
+  ---@param bcol number
+  local function set_text(alnum, acol, blnum, bcol, repl)
+    -- row indices are end-inclusive, and column indices are end-exclusive.
+    vim.api.nvim_buf_set_text(buf, alnum, acol, blnum, bcol, repl)
+
+    local new_last_line_num = self.start.lnum + #replacement - 1
+    local new_last_col = #(replacement[#replacement] or '')
+    if new_last_line_num == start_lnum then new_last_col = new_last_col + start_col - 1 end
+
+    self.stop = Pos.new(buf, new_last_line_num, new_last_col)
+  end
+
+  ---@param alnum number
+  ---@param blnum number
+  local function set_lines(alnum, blnum, repl)
+    -- indexing is zero-based, end-exclusive
+    vim.api.nvim_buf_set_lines(buf, alnum, blnum, false, repl)
+
+    if #repl == 0 then
+      self.stop = nil
+    else
+      local new_last_line_num = start_lnum + #replacement - 1
+      self.stop = Pos.new(self.start.buf, new_last_line_num, Pos.MAX_COL, self.stop.off)
+    end
+    self.mode = 'v'
+  end
+
+  if replace_type == 'insert' then
+    set_text(start_lnum, start_col, start_lnum, start_col, replacement)
+  elseif replace_type == 'region' then
+    -- Fixup the bounds:
+    local last_line = vim.api.nvim_buf_get_lines(buf, stop_lnum - 1, stop_lnum, false)[1] or ''
+    local max_col = #last_line
+    set_text(start_lnum, start_col, stop_lnum - 1, math.min(stop_col, max_col), replacement)
+  elseif replace_type == 'lines' then
+    set_lines(start_lnum, stop_lnum, replacement)
+  else
+    error 'unreachable'
+  end
+end
+
+---@param amount number
+function Range:shrink(amount)
+  local start = self.start
+  local stop = self.stop
+  if stop == nil then return self:clone() end
+
+  for _ = 1, amount do
+    local next_start = start:next(1)
+    local next_stop = stop:next(-1)
+    if next_start == nil or next_stop == nil then return end
+    start = next_start
+    stop = next_stop
+    if next_start > next_stop then break end
+  end
+  if start > stop then stop = nil end
+  return Range.new(start, stop, self.mode)
+end
+
+---@param amount number
+function Range:must_shrink(amount)
+  local shrunk = self:shrink(amount)
+  if shrunk == nil or shrunk:is_empty() then error 'error in Range:must_shrink: Range:shrink() returned nil' end
+  return shrunk
+end
+
+---@param left string
+---@param right string
+function Range:save_to_pos(left, right)
+  if self:is_empty() then
+    self.start:save_to_pos(left)
+    self.start:save_to_pos(right)
+  else
+    self.start:save_to_pos(left)
+    self.stop:save_to_pos(right)
+  end
+end
+
+---@param left string
+---@param right string
+function Range:save_to_marks(left, right)
+  if self:is_empty() then
+    self.start:save_to_mark(left)
+    self.start:save_to_mark(right)
+  else
+    self.start:save_to_mark(left)
+    self.stop:save_to_mark(right)
+  end
+end
+
+function Range:set_visual_selection()
+  if self:is_empty() then return end
+
+  if vim.api.nvim_get_current_buf() ~= self.start.buf then vim.api.nvim_set_current_buf(self.start.buf) end
+
+  State.run(self.start.buf, function(s)
+    s:track_mark 'a'
+    s:track_mark 'b'
+
+    self.start:save_to_mark 'a'
+    self.stop:save_to_mark 'b'
+    local mode = self.mode
+
+    local normal_cmd_args = ''
+    if vim.api.nvim_get_mode().mode == 'n' then normal_cmd_args = normal_cmd_args .. mode end
+    normal_cmd_args = normal_cmd_args .. '`ao`b'
+    vim.cmd { cmd = 'normal', args = { normal_cmd_args }, bang = true }
+
+    return nil
+  end)
+end
+
+---@param group string
+---@param opts? { timeout?: number, priority?: number, on_macro?: boolean }
+function Range:highlight(group, opts)
+  if self:is_empty() then return end
+
+  opts = opts or { on_macro = false }
+  if opts.on_macro == nil then opts.on_macro = false end
+
+  local in_macro = vim.fn.reg_executing() ~= ''
+  if not opts.on_macro and in_macro then return { clear = function() end } end
+
+  local ns = vim.api.nvim_create_namespace ''
+  State.run(self.start.buf, function(s)
+    if not in_macro then s:track_winview() end
+
+    (vim.hl or vim.highlight).range(
+      self.start.buf,
+      ns,
+      group,
+      { self.start.lnum, self.start.col },
+      { self.stop.lnum, self.stop.col },
+      {
+        inclusive = true,
+        priority = opts.priority,
+        regtype = self.mode,
+      }
+    )
+
+    return nil
+  end)
+  vim.cmd.redraw()
+
+  local function clear()
+    vim.api.nvim_buf_clear_namespace(self.start.buf, ns, self.start.lnum, self.stop.lnum + 1)
+    vim.cmd.redraw()
+  end
+  if opts.timeout ~= nil then vim.defer_fn(clear, opts.timeout) end
+
+  return { ns = ns, clear = clear }
+end
+
+return Range

lua/u/renderer.lua

@@ -0,0 +1,438 @@
+local utils = require 'u.utils'
+
+local M = {}
+
+--- @alias Tag { kind: 'tag'; name: string, attributes: table<string, unknown>, children: Tree }
+--- @alias Node nil | boolean | string | Tag
+--- @alias Tree Node | Node[]
+local TagMetaTable = {}
+
+--- @param name string
+--- @param attributes? table<string, any>
+--- @param children? Node | Node[]
+--- @return Tag
+function M.h(name, attributes, children)
+  return setmetatable({
+    kind = 'tag',
+    name = name,
+    attributes = attributes or {},
+    children = children,
+  }, TagMetaTable)
+end
+
+--------------------------------------------------------------------------------
+-- Renderer class
+--------------------------------------------------------------------------------
+--- @alias RendererExtmark { id?: number; start: [number, number]; stop: [number, number]; opts: any; tag: any }
+
+--- @class Renderer
+--- @field bufnr number
+--- @field ns number
+--- @field changedtick number
+--- @field old { lines: string[]; extmarks: RendererExtmark[] }
+--- @field curr { lines: string[]; extmarks: RendererExtmark[] }
+local Renderer = {}
+Renderer.__index = Renderer
+M.Renderer = Renderer
+
+--- @param x any
+--- @return boolean
+function Renderer.is_tag(x) return type(x) == 'table' and getmetatable(x) == TagMetaTable end
+
+--- @param x any
+--- @return boolean
+function Renderer.is_tag_arr(x)
+  if type(x) ~= 'table' then return false end
+  return #x == 0 or not Renderer.is_tag(x)
+end
+
+--- @param bufnr number|nil
+function Renderer.new(bufnr)
+  if bufnr == nil then bufnr = vim.api.nvim_get_current_buf() end
+
+  if vim.b[bufnr]._renderer_ns == nil then
+    vim.b[bufnr]._renderer_ns = vim.api.nvim_create_namespace('my.renderer:' .. tostring(bufnr))
+  end
+
+  local self = setmetatable({
+    bufnr = bufnr,
+    ns = vim.b[bufnr]._renderer_ns,
+    changedtick = 0,
+    old = { lines = {}, extmarks = {} },
+    curr = { lines = {}, extmarks = {} },
+  }, Renderer)
+  return self
+end
+
+--- @param opts {
+---   tree: Tree;
+---   on_tag?: fun(tag: Tag, start0: [number, number], stop0: [number, number]): any;
+--- }
+function Renderer.markup_to_lines(opts)
+  --- @type string[]
+  local lines = {}
+
+  local curr_line1 = 1
+  local curr_col1 = 1 -- exclusive: sits one position **beyond** the last inserted text
+  --- @param s string
+  local function put(s)
+    lines[curr_line1] = (lines[curr_line1] or '') .. s
+    curr_col1 = #lines[curr_line1] + 1
+  end
+  local function put_line()
+    table.insert(lines, '')
+    curr_line1 = curr_line1 + 1
+    curr_col1 = 1
+  end
+
+  --- @param node Node
+  local function visit(node)
+    if node == nil or type(node) == 'boolean' then return end
+
+    if type(node) == 'string' then
+      local node_lines = vim.split(node, '\n')
+      for lnum, s in ipairs(node_lines) do
+        if lnum > 1 then put_line() end
+        put(s)
+      end
+    elseif Renderer.is_tag(node) then
+      local start0 = { curr_line1 - 1, curr_col1 - 1 }
+
+      -- visit the children:
+      if Renderer.is_tag_arr(node.children) then
+        for _, child in ipairs(node.children) do
+          -- newlines are not controlled by array entries, do NOT output a line here:
+          visit(child)
+        end
+      else
+        visit(node.children)
+      end
+
+      local stop0 = { curr_line1 - 1, curr_col1 - 1 }
+      if opts.on_tag then opts.on_tag(node, start0, stop0) end
+    elseif Renderer.is_tag_arr(node) then
+      for _, child in ipairs(node) do
+        -- newlines are not controlled by array entries, do NOT output a line here:
+        visit(child)
+      end
+    end
+  end
+  visit(opts.tree)
+
+  return lines
+end
+
+--- @param opts {
+---   tree: string;
+---   format_tag?: fun(tag: Tag): string;
+--- }
+function Renderer.markup_to_string(opts) return table.concat(Renderer.markup_to_lines(opts), '\n') end
+
+--- @param tree Tree
+function Renderer:render(tree)
+  local changedtick = vim.b[self.bufnr].changedtick
+  if changedtick ~= self.changedtick then
+    self.curr = { lines = vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
+    self.changedtick = changedtick
+  end
+
+  --- @type RendererExtmark[]
+  local extmarks = {}
+
+  --- @type string[]
+  local lines = Renderer.markup_to_lines {
+    tree = tree,
+
+    on_tag = function(tag, start0, stop0)
+      if tag.name == 'text' then
+        local hl = tag.attributes.hl
+        if type(hl) == 'string' then
+          tag.attributes.extmark = tag.attributes.extmark or {}
+          tag.attributes.extmark.hl_group = tag.attributes.extmark.hl_group or hl
+        end
+
+        local extmark = tag.attributes.extmark
+
+        -- Set any necessary keymaps:
+        for _, mode in ipairs { 'i', 'n', 'v', 'x', 'o' } do
+          for lhs, _ in pairs(tag.attributes[mode .. 'map'] or {}) do
+            -- Force creating an extmark if there are key handlers. To accurately
+            -- sense the bounds of the text, we need an extmark:
+            extmark = extmark or {}
+            vim.keymap.set(
+              'n',
+              lhs,
+              function() return self:_on_expr_map('n', lhs) end,
+              { buffer = self.bufnr, expr = true, replace_keycodes = true }
+            )
+          end
+        end
+
+        if extmark then
+          table.insert(extmarks, {
+            start = start0,
+            stop = stop0,
+            opts = extmark,
+            tag = tag,
+          })
+        end
+      end
+    end,
+  }
+
+  self.old = self.curr
+  self.curr = { lines = lines, extmarks = extmarks }
+  self:_reconcile()
+end
+
+--- @private
+--- @param info string
+--- @param start integer
+--- @param end_ integer
+--- @param strict_indexing boolean
+--- @param replacement string[]
+function Renderer:_set_lines(info, start, end_, strict_indexing, replacement)
+  self:_log { 'set_lines', self.bufnr, start, end_, strict_indexing, replacement }
+  vim.api.nvim_buf_set_lines(self.bufnr, start, end_, strict_indexing, replacement)
+  self:_log { 'after(' .. info .. ')', vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
+end
+
+--- @private
+--- @param info string
+--- @param start_row integer
+--- @param start_col integer
+--- @param end_row integer
+--- @param end_col integer
+--- @param replacement string[]
+function Renderer:_set_text(info, start_row, start_col, end_row, end_col, replacement)
+  self:_log { 'set_text', self.bufnr, start_row, start_col, end_row, end_col, replacement }
+  vim.api.nvim_buf_set_text(self.bufnr, start_row, start_col, end_row, end_col, replacement)
+  self:_log { 'after(' .. info .. ')', vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
+end
+
+--- @private
+function Renderer:_log(...)
+  --
+  -- vim.print(...)
+end
+
+--- @private
+function Renderer:_reconcile()
+  local line_changes = utils.levenshtein(self.old.lines, self.curr.lines)
+  self.old = self.curr
+
+  --
+  -- Step 1: morph the text to the desired state:
+  --
+  self:_log { line_changes = line_changes }
+  for _, line_change in ipairs(line_changes) do
+    local lnum0 = line_change.index - 1
+
+    if line_change.kind == 'add' then
+      self:_set_lines('add-line', lnum0, lnum0, true, { line_change.item })
+    elseif line_change.kind == 'change' then
+      -- Compute inter-line diff, and apply:
+      self:_log '--------------------------------------------------------------------------------'
+      local col_changes = utils.levenshtein(vim.split(line_change.from, ''), vim.split(line_change.to, ''))
+
+      for _, col_change in ipairs(col_changes) do
+        local cnum0 = col_change.index - 1
+        self:_log { line_change = col_change, cnum = cnum0, lnum = lnum0 }
+        if col_change.kind == 'add' then
+          self:_set_text('add-char', lnum0, cnum0, lnum0, cnum0, { col_change.item })
+        elseif col_change.kind == 'change' then
+          self:_set_text('change-char', lnum0, cnum0, lnum0, cnum0 + 1, { col_change.to })
+        elseif col_change.kind == 'delete' then
+          self:_set_text('del-char', lnum0, cnum0, lnum0, cnum0 + 1, {})
+        else
+          -- No change
+        end
+      end
+    elseif line_change.kind == 'delete' then
+      self:_set_lines('del-line', lnum0, lnum0 + 1, true, {})
+    else
+      -- No change
+    end
+  end
+  self.changedtick = vim.b[self.bufnr].changedtick
+
+  --
+  -- Step 2: reconcile extmarks:
+  --
+  -- Clear current extmarks:
+  vim.api.nvim_buf_clear_namespace(self.bufnr, self.ns, 0, -1)
+  -- Set current extmarks:
+  for _, extmark in ipairs(self.curr.extmarks) do
+    extmark.id = vim.api.nvim_buf_set_extmark(
+      self.bufnr,
+      self.ns,
+      extmark.start[1],
+      extmark.start[2],
+      vim.tbl_extend('force', {
+        id = extmark.id,
+        end_row = extmark.stop[1],
+        end_col = extmark.stop[2],
+      }, extmark.opts)
+    )
+  end
+end
+
+--- @private
+--- @param mode string
+--- @param lhs string
+function Renderer:_on_expr_map(mode, lhs)
+  -- find the tag with the smallest intersection that contains the cursor:
+  local pos0 = vim.api.nvim_win_get_cursor(0)
+  pos0[1] = pos0[1] - 1 -- make it actually 0-based
+  local pos_infos = self:get_pos_infos(pos0)
+
+  if #pos_infos == 0 then return lhs end
+
+  -- Find the first tag that is listening for this event:
+  local cancel = false
+  for _, pos_info in ipairs(pos_infos) do
+    local tag = pos_info.tag
+
+    -- is the tag listening?
+    local f = vim.tbl_get(tag.attributes, mode .. 'map', lhs)
+    if type(f) == 'function' then
+      local result = f()
+      if result == '' then
+        -- bubble-up to the next tag, but set cancel to true, in case there are
+        -- no more tags to bubble up to:
+        cancel = true
+      else
+        return result
+      end
+    end
+  end
+
+  -- Resort to default behavior:
+  return cancel and '' or lhs
+end
+
+--- Returns pairs of extmarks and tags associate with said extmarks. The
+--- returned tags/extmarks are sorted smallest (innermost) to largest
+--- (outermost).
+---
+--- @private (private for now)
+--- @param pos0 [number; number]
+--- @return { extmark: RendererExtmark; tag: Tag; }[]
+function Renderer:get_pos_infos(pos0)
+  local cursor_line0, cursor_col0 = pos0[1], pos0[2]
+
+  -- The cursor (block) occupies **two** extmark spaces: one for it's left
+  -- edge, and one for it's right. We need to do our own intersection test,
+  -- because the NeoVim API is over-inclusive in what it returns:
+  --- @type RendererExtmark[]
+  local intersecting_extmarks = vim
+    .iter(vim.api.nvim_buf_get_extmarks(self.bufnr, self.ns, pos0, pos0, { details = true, overlap = true }))
+    --- @return RendererExtmark
+    :map(function(ext)
+      --- @type number, number, number, { end_row?: number; end_col?: number }|nil
+      local id, line0, col0, details = unpack(ext)
+      local start = { line0, col0 }
+      local stop = { line0, col0 }
+      if details and details.end_row ~= nil and details.end_col ~= nil then
+        stop = { details.end_row, details.end_col }
+      end
+      return { id = id, start = start, stop = stop, opts = details }
+    end)
+    --- @param ext RendererExtmark
+    :filter(function(ext)
+      if ext.stop[1] ~= nil and ext.stop[2] ~= nil then
+        return cursor_line0 >= ext.start[1]
+          and cursor_col0 >= ext.start[2]
+          and cursor_line0 <= ext.stop[1]
+          and cursor_col0 < ext.stop[2]
+      else
+        return true
+      end
+    end)
+    :totable()
+
+  -- Sort the tags into smallest (inner) to largest (outer):
+  table.sort(
+    intersecting_extmarks,
+    --- @param x1 RendererExtmark
+    --- @param x2 RendererExtmark
+    function(x1, x2)
+      if
+        x1.start[1] == x2.start[1]
+        and x1.start[2] == x2.start[2]
+        and x1.stop[1] == x2.stop[1]
+        and x1.stop[2] == x2.stop[2]
+      then
+        return x1.id < x2.id
+      end
+
+      return x1.start[1] >= x2.start[1]
+        and x1.start[2] >= x2.start[2]
+        and x1.stop[1] <= x2.stop[1]
+        and x1.stop[2] <= x2.stop[2]
+    end
+  )
+
+  -- When we set the extmarks in the step above, we captured the IDs of the
+  -- created extmarks in self.curr.extmarks, which also has which tag each
+  -- extmark is associated with. Cross-reference with that list to get a list
+  -- of tags that we need to fire events for:
+  --- @type { extmark: RendererExtmark; tag: Tag }[]
+  local matching_tags = vim
+    .iter(intersecting_extmarks)
+    --- @param ext RendererExtmark
+    :map(function(ext)
+      for _, extmark_cache in ipairs(self.curr.extmarks) do
+        if extmark_cache.id == ext.id then return { extmark = ext, tag = extmark_cache.tag } end
+      end
+    end)
+    :totable()
+
+  return matching_tags
+end
+
+--------------------------------------------------------------------------------
+-- TreeBuilder class
+--------------------------------------------------------------------------------
+
+--- @class TreeBuilder
+--- @field private nodes Node[]
+local TreeBuilder = {}
+TreeBuilder.__index = TreeBuilder
+M.TreeBuilder = TreeBuilder
+
+function TreeBuilder.new()
+  local self = setmetatable({ nodes = {} }, TreeBuilder)
+  return self
+end
+
+--- @param nodes Tree
+--- @return TreeBuilder
+function TreeBuilder:put(nodes)
+  table.insert(self.nodes, nodes)
+  return self
+end
+
+--- @param name string
+--- @param attributes? table<string, any>
+--- @param children? Node | Node[]
+--- @return TreeBuilder
+function TreeBuilder:put_h(name, attributes, children)
+  local tag = M.h(name, attributes, children)
+  table.insert(self.nodes, tag)
+  return self
+end
+
+--- @param fn fun(TreeBuilder): any
+--- @return TreeBuilder
+function TreeBuilder:nest(fn)
+  local nested_writer = TreeBuilder.new()
+  fn(nested_writer)
+  table.insert(self.nodes, nested_writer.nodes)
+  return self
+end
+
+--- @return Tree
+function TreeBuilder:tree() return self.nodes end
+
+return M

lua/u/repeat.lua

@@ -0,0 +1,61 @@
+local M = {}
+
+local function _normal(cmd) vim.cmd.normal { cmd = 'normal', args = { cmd }, bang = true } end
+
+M.native_repeat = function() _normal '.' end
+M.native_undo = function() _normal 'u' end
+
+local function update_ts() vim.b.tt_changedtick = vim.b.changedtick end
+
+---@param cmd? string|fun():unknown
+function M.set(cmd)
+  update_ts()
+  if cmd ~= nil then vim.b.tt_repeatcmd = cmd end
+end
+
+local function tt_was_last_repeatable()
+  local ts, tt_ts = vim.b.changedtick, vim.b.tt_changedtick
+  return tt_ts ~= nil and ts <= tt_ts
+end
+
+---@generic T
+---@param cmd string|fun():T
+---@return T
+function M.run(cmd)
+  M.set(cmd)
+  local result = cmd()
+  update_ts()
+  return result
+end
+
+function M.do_repeat()
+  local tt_cmd = vim.b.tt_repeatcmd
+  if not tt_was_last_repeatable() or (type(tt_cmd) ~= 'function' and type(tt_cmd) ~= 'string') then
+    return M.native_repeat()
+  end
+
+  -- execute the cached command:
+  local count = vim.api.nvim_get_vvar 'count1'
+  if type(tt_cmd) == 'string' then
+    _normal(count .. tt_cmd --[[@as string]])
+  else
+    local last_return
+    for _ = 1, count do
+      last_return = M.run(tt_cmd --[[@as fun():any]])
+    end
+    return last_return
+  end
+end
+
+function M.undo()
+  local tt_was_last_repeatable_before_undo = tt_was_last_repeatable()
+  M.native_undo()
+  if tt_was_last_repeatable_before_undo then update_ts() end
+end
+
+function M.setup()
+  vim.keymap.set('n', '.', M.do_repeat)
+  vim.keymap.set('n', 'u', M.undo)
+end
+
+return M

lua/u/state.lua

@@ -0,0 +1,90 @@
+---@class State
+---@field buf number
+---@field registers table
+---@field marks table
+---@field positions table
+---@field keymaps { mode: string; lhs: any, rhs: any, buffer?: number }[]
+---@field global_options table<string, any>
+---@field win_view vim.fn.winsaveview.ret|nil
+local State = {}
+
+---@param buf number
+---@return State
+function State.new(buf)
+  if buf == 0 then buf = vim.api.nvim_get_current_buf() end
+  local s = { buf = buf, registers = {}, marks = {}, positions = {}, keymaps = {}, global_options = {} }
+  setmetatable(s, { __index = State })
+  return s
+end
+
+---@generic T
+---@param buf number
+---@param f fun(s: State):T
+---@return T
+function State.run(buf, f)
+  local s = State.new(buf)
+  local ok, result = pcall(f, s)
+  s:restore()
+  if not ok then error(result) end
+  return result
+end
+
+---@param buf number
+---@param f fun(s: State, callback: fun(): any):any
+---@param callback fun():any
+function State.run_async(buf, f, callback)
+  local s = State.new(buf)
+  f(s, function()
+    s:restore()
+    callback()
+  end)
+end
+
+function State:track_keymap(mode, lhs)
+  local old =
+    -- Look up the mapping in buffer-local maps:
+    vim.iter(vim.api.nvim_buf_get_keymap(self.buf, mode)):find(function(map) return map.lhs == lhs end)
+    -- Look up the mapping in global maps:
+    or vim.iter(vim.api.nvim_get_keymap(mode)):find(function(map) return map.lhs == lhs end)
+
+  -- Did we find a mapping?
+  if old == nil then return end
+
+  -- Track it:
+  table.insert(self.keymaps, { mode = mode, lhs = lhs, rhs = old.rhs or old.callback, buffer = old.buffer })
+end
+
+---@param reg string
+function State:track_register(reg) self.registers[reg] = vim.fn.getreg(reg) end
+
+---@param mark string
+function State:track_mark(mark) self.marks[mark] = vim.api.nvim_buf_get_mark(self.buf, mark) end
+
+---@param pos string
+function State:track_pos(pos) self.positions[pos] = vim.fn.getpos(pos) end
+
+---@param nm string
+function State:track_global_option(nm) self.global_options[nm] = vim.g[nm] end
+
+function State:track_winview() self.win_view = vim.fn.winsaveview() end
+
+function State:restore()
+  for reg, val in pairs(self.registers) do
+    vim.fn.setreg(reg, val)
+  end
+  for mark, val in pairs(self.marks) do
+    vim.api.nvim_buf_set_mark(self.buf, mark, val[1], val[2], {})
+  end
+  for pos, val in pairs(self.positions) do
+    vim.fn.setpos(pos, val)
+  end
+  for _, map in ipairs(self.keymaps) do
+    vim.keymap.set(map.mode, map.lhs, map.rhs, { buffer = map.buffer })
+  end
+  for nm, val in pairs(self.global_options) do
+    vim.g[nm] = val
+  end
+  if self.win_view ~= nil then vim.fn.winrestview(self.win_view) end
+end
+
+return State

lua/u/tracker.lua

@@ -0,0 +1,301 @@
+local M = {}
+
+M.debug = false
+
+--------------------------------------------------------------------------------
+-- class Signal
+--------------------------------------------------------------------------------
+
+--- @class Signal
+--- @field name? string
+--- @field private changing boolean
+--- @field private value any
+--- @field private subscribers table<function, boolean>
+--- @field private on_dispose_callbacks function[]
+local Signal = {}
+M.Signal = Signal
+Signal.__index = Signal
+
+--- @param value any
+--- @param name? string
+--- @return Signal
+function Signal:new(value, name)
+  local obj = setmetatable({
+    name = name,
+    changing = false,
+    value = value,
+    subscribers = {},
+    on_dispose_callbacks = {},
+  }, self)
+  return obj
+end
+
+--- @param value any
+function Signal:set(value)
+  self.value = value
+
+  -- We don't handle cyclic updates:
+  if self.changing then
+    if M.debug then
+      vim.notify('circular dependency detected' .. (self.name and (' in ' .. self.name) or ''), vim.log.levels.WARN)
+    end
+    return
+  end
+
+  local prev_changing = self.changing
+  self.changing = true
+  local ok = true
+  local err = nil
+  for _, cb in ipairs(self.subscribers) do
+    local ok2, err2 = pcall(cb, value)
+    if not ok2 then
+      ok = false
+      err = err or err2
+    end
+  end
+  self.changing = prev_changing
+
+  if not ok then
+    vim.notify(
+      'error notifying' .. (self.name and (' in ' .. self.name) or '') .. ': ' .. tostring(err),
+      vim.log.levels.WARN
+    )
+    error(err)
+  end
+end
+
+function Signal:schedule_set(value)
+  vim.schedule(function() self:set(value) end)
+end
+
+--- @return any
+function Signal:get()
+  local ctx = M.ExecutionContext.current()
+  if ctx then ctx:track(self) end
+  return self.value
+end
+
+--- @param fn function
+function Signal:update(fn) self:set(fn(self.value)) end
+
+--- @param fn function
+function Signal:schedule_update(fn) self:schedule_set(fn(self.value)) end
+
+--- @generic U
+--- @param fn fun(value: T): U
+--- @return Signal --<U>
+function Signal:map(fn)
+  local mapped_signal = M.create_memo(function()
+    local value = self:get()
+    return fn(value)
+  end, self.name and self.name .. ':mapped' or nil)
+  return mapped_signal
+end
+
+--- @return Signal
+function Signal:clone()
+  return self:map(function(x) return x end)
+end
+
+--- @param fn fun(value: T): boolean
+--- @return Signal -- <T>
+function Signal:filter(fn)
+  local filtered_signal = M.create_signal(nil, self.name and self.name .. ':filtered' or nil)
+  local unsubscribe_from_self = self:subscribe(function(value)
+    if fn(value) then filtered_signal:set(value) end
+  end)
+  filtered_signal:on_dispose(unsubscribe_from_self)
+  return filtered_signal
+end
+
+--- @param ms number
+--- @return Signal -- <T>
+function Signal:debounce(ms)
+  local function set_timeout(timeout, callback)
+    local timer = (vim.uv or vim.loop).new_timer()
+    timer:start(timeout, 0, function()
+      timer:stop()
+      timer:close()
+      callback()
+    end)
+    return timer
+  end
+
+  local filtered = M.create_signal(self.value, self.name and self.name .. ':debounced' or nil)
+
+  --- @type {
+  --   queued: { value: T, ts: number }[]
+  --   timer?: uv_timer_t
+  -- }
+  local state = { queued = {}, timer = nil }
+  local function clear_timeout()
+    if state.timer == nil then return end
+    pcall(function()
+      state.timer:stop()
+      state.timer:close()
+    end)
+    state.timer = nil
+  end
+
+  local unsubscribe_from_self = self:subscribe(function(value)
+    -- Stop any previously running timer:
+    if state.timer then clear_timeout() end
+    local now_ms = (vim.uv or vim.loop).hrtime() / 1e6
+
+    -- If there is anything older than `ms` in our queue, emit it:
+    local older_than_ms = vim.iter(state.queued):filter(function(item) return now_ms - item.ts > ms end):totable()
+    local last_older_than_ms = older_than_ms[#older_than_ms]
+    if last_older_than_ms then
+      filtered:set(last_older_than_ms.value)
+      state.queued = {}
+    end
+
+    -- overwrite anything young enough
+    table.insert(state.queued, { value = value, ts = now_ms })
+    state.timer = set_timeout(ms, function()
+      vim.schedule(function() filtered:set(value) end)
+      -- If a timer was allowed to run to completion, that means that no other
+      -- item has been queued, since the timer is reset every time a new item
+      -- comes in. This means we can reset the queue
+      clear_timeout()
+      state.queued = {}
+    end)
+  end)
+  filtered:on_dispose(unsubscribe_from_self)
+
+  return filtered
+end
+
+--- @param callback function
+function Signal:subscribe(callback)
+  table.insert(self.subscribers, callback)
+  return function() self:unsubscribe(callback) end
+end
+
+--- @param callback function
+function Signal:on_dispose(callback) table.insert(self.on_dispose_callbacks, callback) end
+
+--- @param callback function
+function Signal:unsubscribe(callback)
+  for i, cb in ipairs(self.subscribers) do
+    if cb == callback then
+      table.remove(self.subscribers, i)
+      break
+    end
+  end
+end
+
+function Signal:dispose()
+  self.subscribers = {}
+  for _, callback in ipairs(self.on_dispose_callbacks) do
+    callback()
+  end
+end
+
+--------------------------------------------------------------------------------
+-- class ExecutionContext
+--------------------------------------------------------------------------------
+
+CURRENT_CONTEXT = nil
+
+--- @class ExecutionContext
+--- @field signals table<Signal, boolean>
+local ExecutionContext = {}
+M.ExecutionContext = ExecutionContext
+ExecutionContext.__index = ExecutionContext
+
+--- @return ExecutionContext
+function ExecutionContext:new()
+  return setmetatable({
+    signals = {},
+    subscribers = {},
+  }, ExecutionContext)
+end
+
+function ExecutionContext.current() return CURRENT_CONTEXT end
+
+--- @param fn function
+--- @param ctx ExecutionContext
+function ExecutionContext:run(fn, ctx)
+  local oldCtx = CURRENT_CONTEXT
+  CURRENT_CONTEXT = ctx
+  local result
+  local success, err = pcall(function() result = fn() end)
+
+  CURRENT_CONTEXT = oldCtx
+
+  if not success then error(err) end
+
+  return result
+end
+
+function ExecutionContext:track(signal) self.signals[signal] = true end
+
+--- @param callback function
+function ExecutionContext:subscribe(callback)
+  local wrapped_callback = function() callback() end
+  for signal in pairs(self.signals) do
+    signal:subscribe(wrapped_callback)
+  end
+
+  return function()
+    for signal in pairs(self.signals) do
+      signal:unsubscribe(wrapped_callback)
+    end
+  end
+end
+
+function ExecutionContext:dispose()
+  for signal, _ in pairs(self.signals) do
+    signal:dispose()
+  end
+  self.signals = {}
+end
+
+--------------------------------------------------------------------------------
+-- Helpers
+--------------------------------------------------------------------------------
+
+--- @param value any
+--- @param name? string
+--- @return Signal
+function M.create_signal(value, name) return Signal:new(value, name) end
+
+--- @param fn function
+--- @param name? string
+--- @return Signal
+function M.create_memo(fn, name)
+  --- @type Signal
+  local result
+  local unsubscribe = M.create_effect(function()
+    local value = fn()
+    if name and M.debug then vim.notify(name) end
+    if result then
+      result:set(value)
+    else
+      result = M.create_signal(value, name and ('m.s:' .. name) or nil)
+    end
+  end, name)
+  result:on_dispose(unsubscribe)
+  return result
+end
+
+--- @param fn function
+--- @param name? string
+function M.create_effect(fn, name)
+  local ctx = M.ExecutionContext:new()
+  M.ExecutionContext:run(fn, ctx)
+  return ctx:subscribe(function()
+    if name and M.debug then
+      local deps = vim
+        .iter(vim.tbl_keys(ctx.signals))
+        :map(function(s) return s.name end)
+        :filter(function(nm) return nm ~= nil end)
+        :join ','
+      vim.notify(name .. '(deps=' .. deps .. ')')
+    end
+    fn()
+  end)
+end
+
+return M

lua/u/utils.lua

@@ -0,0 +1,215 @@
+local M = {}
+
+--
+-- Types
+--
+
+---@alias QfItem { col: number, filename: string, kind: string, lnum: number, text: string }
+---@alias KeyMaps table<string, fun(): any | string> }
+---@alias CmdArgs { args: string; bang: boolean; count: number; fargs: string[]; line1: number; line2: number; mods: string; name: string; range: 0|1|2; reg: string; smods: any; info: Range|nil }
+
+--- @generic T
+--- @param x `T`
+--- @param message? string
+--- @return T
+function M.dbg(x, message)
+  local t = {}
+  if message ~= nil then table.insert(t, message) end
+  table.insert(t, x)
+  vim.print(t)
+  return x
+end
+
+--- A utility for creating user commands that also pre-computes useful information
+--- and attaches it to the arguments.
+---
+--- ```lua
+--- -- Example:
+--- ucmd('MyCmd', function(args)
+---   -- print the visually selected text:
+---   vim.print(args.info:text())
+---   -- or get the vtext as an array of lines:
+---   vim.print(args.info:lines())
+--- end, { nargs = '*', range = true })
+--- ```
+---@param name string
+---@param cmd string | fun(args: CmdArgs): any
+---@param opts? { nargs?: 0|1|'*'|'?'|'+'; range?: boolean|'%'|number; count?: boolean|number, addr?: string; completion?: string }
+function M.ucmd(name, cmd, opts)
+  local Range = require 'u.range'
+
+  opts = opts or {}
+  local cmd2 = cmd
+  if type(cmd) == 'function' then
+    cmd2 = function(args)
+      args.info = Range.from_cmd_args(args)
+      return cmd(args)
+    end
+  end
+  vim.api.nvim_create_user_command(name, cmd2, opts or {})
+end
+
+---@param key_seq string
+---@param fn fun(key_seq: string):Range|Pos|nil
+---@param opts? { buffer: number|nil }
+function M.define_text_object(key_seq, fn, opts)
+  local Range = require 'u.range'
+  local Pos = require 'u.pos'
+
+  if opts ~= nil and opts.buffer == 0 then opts.buffer = vim.api.nvim_get_current_buf() end
+
+  local function handle_visual()
+    local range_or_pos = fn(key_seq)
+    if range_or_pos == nil then return end
+    if Range.is(range_or_pos) and range_or_pos:is_empty() then range_or_pos = range_or_pos.start end
+
+    if Range.is(range_or_pos) then
+      local range = range_or_pos --[[@as Range]]
+      range:set_visual_selection()
+    else
+      vim.cmd { cmd = 'normal', args = { '<Esc>' }, bang = true }
+    end
+  end
+  vim.keymap.set({ 'x' }, key_seq, handle_visual, opts and { buffer = opts.buffer } or nil)
+
+  local function handle_normal()
+    local State = require 'u.state'
+
+    -- enter visual mode:
+    vim.cmd { cmd = 'normal', args = { 'v' }, bang = true }
+
+    local range_or_pos = fn(key_seq)
+    if range_or_pos == nil then return end
+    if Range.is(range_or_pos) and range_or_pos:is_empty() then range_or_pos = range_or_pos.start end
+
+    if Range.is(range_or_pos) then
+      range_or_pos:set_visual_selection()
+    elseif Pos.is(range_or_pos) then
+      local p = range_or_pos --[[@as Pos]]
+      State.run(0, function(s)
+        s:track_global_option 'eventignore'
+        vim.opt_global.eventignore = 'all'
+
+        -- insert a single space, so we can select it:
+        vim.api.nvim_buf_set_text(0, p.lnum, p.col, p.lnum, p.col, { ' ' })
+        -- select the space:
+        Range.new(p, p, 'v'):set_visual_selection()
+      end)
+    end
+  end
+  vim.keymap.set({ 'o' }, key_seq, handle_normal, opts and { buffer = opts.buffer } or nil)
+end
+
+---@type fun(): nil|(fun():any)
+local __U__RepeatableOpFunc_rhs = nil
+
+--- This is the global utility function used for operatorfunc
+--- in repeatablemap
+---@type nil|fun(range: Range): fun():any|nil
+-- selene: allow(unused_variable)
+function __U__RepeatableOpFunc()
+  if __U__RepeatableOpFunc_rhs ~= nil then __U__RepeatableOpFunc_rhs() end
+end
+
+function M.repeatablemap(mode, lhs, rhs, opts)
+  vim.keymap.set(mode, lhs, function()
+    __U__RepeatableOpFunc_rhs = rhs
+    vim.o.operatorfunc = 'v:lua.__U__RepeatableOpFunc'
+    return 'g@ '
+  end, vim.tbl_extend('force', opts or {}, { expr = true }))
+end
+
+function M.get_editor_dimensions() return { width = vim.go.columns, height = vim.go.lines } end
+
+--- @alias LevenshteinChange<T> ({ kind: 'add'; item: T; index: number; } | { kind: 'delete'; item: T; index: number; } | { kind: 'change'; from: T; to: T; index: number; })
+--- @private
+--- @generic T
+--- @param x `T`[]
+--- @param y T[]
+--- @param cost? { of_delete?: fun(x: T): number; of_add?: fun(x: T): number; of_change?: fun(x: T, y: T): number; }
+--- @return LevenshteinChange<T>[]
+function M.levenshtein(x, y, cost)
+  cost = cost or {}
+  local cost_of_delete_f = cost.of_delete or function() return 1 end
+  local cost_of_add_f = cost.of_add or function() return 1 end
+  local cost_of_change_f = cost.of_change or function() return 1 end
+
+  local m, n = #x, #y
+  -- Initialize the distance matrix
+  local dp = {}
+  for i = 0, m do
+    dp[i] = {}
+    for j = 0, n do
+      dp[i][j] = 0
+    end
+  end
+
+  -- Fill the base cases
+  for i = 0, m do
+    dp[i][0] = i
+  end
+  for j = 0, n do
+    dp[0][j] = j
+  end
+
+  -- Compute the Levenshtein distance dynamically
+  for i = 1, m do
+    for j = 1, n do
+      if x[i] == y[j] then
+        dp[i][j] = dp[i - 1][j - 1] -- no cost if items are the same
+      else
+        local costDelete = dp[i - 1][j] + cost_of_delete_f(x[i])
+        local costAdd = dp[i][j - 1] + cost_of_add_f(y[j])
+        local costChange = dp[i - 1][j - 1] + cost_of_change_f(x[i], y[j])
+        dp[i][j] = math.min(costDelete, costAdd, costChange)
+      end
+    end
+  end
+
+  -- Backtrack to find the changes
+  local i = m
+  local j = n
+  --- @type LevenshteinChange[]
+  local changes = {}
+
+  while i > 0 or j > 0 do
+    local default_cost = dp[i][j]
+    local cost_of_change = (i > 0 and j > 0) and dp[i - 1][j - 1] or default_cost
+    local cost_of_add = j > 0 and dp[i][j - 1] or default_cost
+    local cost_of_delete = i > 0 and dp[i - 1][j] or default_cost
+
+    --- @param u number
+    --- @param v number
+    --- @param w number
+    local function is_first_min(u, v, w) return u <= v and u <= w end
+
+    if is_first_min(cost_of_change, cost_of_add, cost_of_delete) then
+      -- potential change
+      if x[i] ~= y[j] then
+        --- @type LevenshteinChange
+        local change = { kind = 'change', from = x[i], index = i, to = y[j] }
+        table.insert(changes, change)
+      end
+      i = i - 1
+      j = j - 1
+    elseif is_first_min(cost_of_add, cost_of_change, cost_of_delete) then
+      -- addition
+      --- @type LevenshteinChange
+      local change = { kind = 'add', item = y[j], index = i + 1 }
+      table.insert(changes, change)
+      j = j - 1
+    elseif is_first_min(cost_of_delete, cost_of_change, cost_of_add) then
+      -- deletion
+      --- @type LevenshteinChange
+      local change = { kind = 'delete', item = x[i], index = i }
+      table.insert(changes, change)
+      i = i - 1
+    else
+      error 'unreachable'
+    end
+  end
+
+  return changes
+end
+
+return M

mise.toml

@@ -1,107 +0,0 @@
-################################################################################
-## Tool Alias
-################################################################################
-
-################################################################################
-## Tools
-################################################################################
-
-[tools]
-# nvimv needs jq:
-jq = "1.8.1"
-"asdf:mise-plugins/mise-lua" = "5.1.5"
-# Since we have busted configured to look for "nvim", have a "default" version
-# installed. In the tests, we will override with `eval $(nvimv env VERSION)`,
-# but to avoid having to litter a bunch of commands with that environment
-# initialization, this just makes things simpler:
-neovim = "0.12.1"
-stylua = "2.3.1"
-"cargo:emmylua_ls" = "0.20.0"
-"cargo:emmylua_check" = "0.20.0"
-
-################################################################################
-# Env
-################################################################################
-
-[env]
-ASDF_LUA_LUAROCKS_VERSION = "3.12.2"
-_.source = { path = "./scripts/env.sh", tools = true }
-
-################################################################################
-# Tasks
-################################################################################
-
-[tasks]
-lint = "emmylua_check --ignore '.prefix/**/*.*' ."
-fmt = "stylua ."
-"fmt:check" = "stylua --check ."
-"test:prepare" = '''
-# Install Lua test dependencies (busted, etc.):
-luarocks test --prepare
-echo
-
-# Check that the nightly version of Neovim is not more than a day old:
-if find .prefix -path '**/nightly/**/nvim' -mtime -1 2>/dev/null | grep -q .; then
-  echo "Neovim Nightly is up-to-date"
-else
-  if ./nvimv/nvimv ls | grep nightly >/dev/null; then
-    ./nvimv/nvimv upgrade nightly
-  else
-    ./nvimv/nvimv install nightly
-  fi
-fi
-echo
-'''
-
-[tasks."test:version:no-prep"]
-hide = true
-usage = '''
-arg "<version>" help="The version of Neovim to test with"
-'''
-run = '''
-echo
-echo -----------------------------
-echo -----------------------------
-echo Neovim version=$usage_version
-echo -----------------------------
-echo -----------------------------
-echo
-./nvimv/nvimv install $usage_version
-eval $(./nvimv/nvimv env $usage_version)
-busted --verbose
-'''
-
-[tasks."test:version"]
-depends = ["test:prepare"]
-usage = '''
-arg "<version>" help="The version of Neovim to test with"
-'''
-run = 'mise test:version:no-prep $usage_version'
-
-[tasks."test"]
-run = 'mise test:version 0.12.1'
-
-[tasks."test:all"]
-depends = ["test:prepare"]
-run = '''
-VERSIONS="0.11.5 0.12.1 nightly"
-for v in $VERSIONS; do
-  mise test:version:no-prep $v
-done
-'''
-
-[tasks."test:coverage"]
-depends = ["test:prepare"]
-run = '''
-rm -f ./luacov.*.*
-busted --coverage --verbose
-luacov
-awk '/^Summary$/{flag=1;next} flag{print}' luacov.report.out
-'''
-
-[tasks."ci"]
-run = '''
-mise run fmt:check
-mise run lint
-mise run test:all
-'''

scripts/env.sh

@@ -1,6 +0,0 @@
-#!/usr/bin/env bash
-
-export PREFIX="$(pwd)/.prefix"
-export VIMRUNTIME="$(nvim -u NORC --headless +'echo $VIMRUNTIME' +'quitall' 2>&1)"
-
-eval $(luarocks path)

scripts/make-artifact-tag.sh

@@ -1,43 +0,0 @@
-#!/usr/bin/env bash
-#
-# After tagging a release (say, v1.2.3), use this script to publish
-# lua/u.lua in an artifact branch: artifact-v1.2.3:init.lua. To do so,
-# invoke the script from the root of the repo like so:
-#
-# ./scripts/make-artifact-tag.sh v1.2.3
-#
-# This will create a temporary orphan branch, tag it and immediately delete the
-# branch.
-#
-set -euo pipefail
-
-if [[ $# -ne 1 ]]; then
-  echo "Usage: $0 <TAG>"
-  exit 1
-fi
-
-TAG="$1"
-if [[ "$(echo "$TAG" | awk '/^v[0-9]+\.[0-9]+\.[0-9]+$/ { print "YES" }')" != "YES" ]]; then
-  echo "Invalid tag name: expected 'vX.Y.Z'"
-  exit 1
-fi
-
-ARTIFACT_TAG="artifact-$TAG"
-EXISTING_ARTIFACT_TAG=$(git tag -l "$ARTIFACT_TAG")
-
-if [[ "$ARTIFACT_TAG" = "$EXISTING_ARTIFACT_TAG" ]]; then
-  echo "Artifact tag already exists"
-  exit 1
-fi
-
-git worktree add --orphan -b "$ARTIFACT_TAG" "$ARTIFACT_TAG"
-git cat-file -p "$TAG":lua/u.lua > "$ARTIFACT_TAG"/init.lua
-
-pushd "$ARTIFACT_TAG"
-git add --all
-git commit --message "$ARTIFACT_TAG"
-git tag "$ARTIFACT_TAG"
-popd
-
-git worktree remove -f "$ARTIFACT_TAG"
-git branch -D "$ARTIFACT_TAG"

selene.toml

@@ -0,0 +1,4 @@
+std = "vim"
+
+[lints]
+multiple_statements = "allow"

spec/buffer_spec.lua

@@ -0,0 +1,30 @@
+local Buffer = require 'u.buffer'
+local withbuf = loadfile './spec/withbuf.lua'()
+
+describe('Buffer', function()
+  it('should replace all lines', function()
+    withbuf({}, function()
+      local buf = Buffer.from_nr()
+      buf:all():replace 'bleh'
+      local actual_lines = vim.api.nvim_buf_get_lines(buf.buf, 0, -1, false)
+      assert.are.same({ 'bleh' }, actual_lines)
+    end)
+  end)
+
+  it('should replace all but first and last lines', function()
+    withbuf({
+      'one',
+      'two',
+      'three',
+    }, function()
+      local buf = Buffer.from_nr()
+      buf:lines(1, -2):replace 'too'
+      local actual_lines = vim.api.nvim_buf_get_lines(buf.buf, 0, -1, false)
+      assert.are.same({
+        'one',
+        'too',
+        'three',
+      }, actual_lines)
+    end)
+  end)
+end)

spec/codewriter_spec.lua

@@ -0,0 +1,29 @@
+local CodeWriter = require 'u.codewriter'
+
+describe('CodeWriter', function()
+  it('should write with indentation', function()
+    local cw = CodeWriter.new()
+    cw:write '{'
+    cw:indent(function(cw2) cw2:write 'x: 123' end)
+    cw:write '}'
+
+    assert.are.same(cw.lines, { '{', '  x: 123', '}' })
+  end)
+
+  it('should keep relative indentation', function()
+    local cw = CodeWriter.new()
+    cw:write '{'
+    cw:indent(function(cw2)
+      cw2:write 'x: 123'
+      cw2:write '  y: 123'
+    end)
+    cw:write '}'
+
+    assert.are.same(cw.lines, {
+      '{',
+      '  x: 123',
+      '    y: 123',
+      '}',
+    })
+  end)
+end)

spec/pos_spec.lua

@@ -0,0 +1,69 @@
+local Pos = require 'u.pos'
+local withbuf = loadfile './spec/withbuf.lua'()
+
+describe('Pos', function()
+  it('get a char from a given position', function()
+    withbuf({ 'asdf', 'bleh', 'a', '', 'goo' }, function()
+      assert.are.same('a', Pos.new(nil, 0, 0):char())
+      assert.are.same('d', Pos.new(nil, 0, 2):char())
+      assert.are.same('f', Pos.new(nil, 0, 3):char())
+      assert.are.same('a', Pos.new(nil, 2, 0):char())
+      assert.are.same('', Pos.new(nil, 3, 0):char())
+      assert.are.same('o', Pos.new(nil, 4, 2):char())
+    end)
+  end)
+
+  it('comparison operators', function()
+    local a = Pos.new(0, 0, 0, 0)
+    local b = Pos.new(0, 1, 0, 0)
+    assert.are.same(a == a, true)
+    assert.are.same(a < b, true)
+  end)
+
+  it('get the next position', function()
+    withbuf({ 'asdf', 'bleh', 'a', '', 'goo' }, function()
+      -- line 1: a => s
+      assert.are.same(Pos.new(nil, 0, 1), Pos.new(nil, 0, 0):next())
+      -- line 1: d => f
+      assert.are.same(Pos.new(nil, 0, 3), Pos.new(nil, 0, 2):next())
+      -- line 1 => 2
+      assert.are.same(Pos.new(nil, 1, 0), Pos.new(nil, 0, 3):next())
+      -- line 3 => 4
+      assert.are.same(Pos.new(nil, 3, 0), Pos.new(nil, 2, 0):next())
+      -- line 4 => 5
+      assert.are.same(Pos.new(nil, 4, 0), Pos.new(nil, 3, 0):next())
+      -- end returns nil
+      assert.are.same(nil, Pos.new(nil, 4, 2):next())
+    end)
+  end)
+
+  it('get the previous position', function()
+    withbuf({ 'asdf', 'bleh', 'a', '', 'goo' }, function()
+      -- line 1: s => a
+      assert.are.same(Pos.new(nil, 0, 0), Pos.new(nil, 0, 1):next(-1))
+      -- line 1: f => d
+      assert.are.same(Pos.new(nil, 0, 2), Pos.new(nil, 0, 3):next(-1))
+      -- line 2 => 1
+      assert.are.same(Pos.new(nil, 0, 3), Pos.new(nil, 1, 0):next(-1))
+      -- line 4 => 3
+      assert.are.same(Pos.new(nil, 2, 0), Pos.new(nil, 3, 0):next(-1))
+      -- line 5 => 4
+      assert.are.same(Pos.new(nil, 3, 0), Pos.new(nil, 4, 0):next(-1))
+      -- beginning returns nil
+      assert.are.same(nil, Pos.new(nil, 0, 0):next(-1))
+    end)
+  end)
+
+  it('find matching brackets', function()
+    withbuf({ 'asdf ({} def <[{}]>) ;lkj' }, function()
+      -- outer parens are matched:
+      assert.are.same(Pos.new(nil, 0, 19), Pos.new(nil, 0, 5):find_match())
+      -- outer parens are matched (backward):
+      assert.are.same(Pos.new(nil, 0, 5), Pos.new(nil, 0, 19):find_match())
+      -- no potential match returns nil
+      assert.are.same(nil, Pos.new(nil, 0, 0):find_match())
+      -- watchdog expires before an otherwise valid match is found:
+      assert.are.same(nil, Pos.new(nil, 0, 5):find_match(2))
+    end)
+  end)
+end)

spec/range_spec.lua

@@ -0,0 +1,560 @@
+local Range = require 'u.range'
+local Pos = require 'u.pos'
+local withbuf = loadfile './spec/withbuf.lua'()
+
+describe('Range', function()
+  it('get text in buffer', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.from_buf_text()
+      local lines = range:lines()
+      assert.are.same({
+        'line one',
+        'and line two',
+      }, lines)
+
+      local text = range:text()
+      assert.are.same('line one\nand line two', text)
+    end)
+
+    withbuf({}, function()
+      local range = Range.from_buf_text()
+      local lines = range:lines()
+      assert.are.same({ '' }, lines)
+
+      local text = range:text()
+      assert.are.same('', text)
+    end)
+  end)
+
+  it('get from positions: v in single line', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 0, 3), 'v')
+      local lines = range:lines()
+      assert.are.same({ 'ine' }, lines)
+
+      local text = range:text()
+      assert.are.same('ine', text)
+    end)
+  end)
+
+  it('get from positions: v across multiple lines', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 2, 4), 'v')
+      local lines = range:lines()
+      assert.are.same({ 'quick brown fox', 'jumps' }, lines)
+    end)
+  end)
+
+  it('get from positions: V', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, Pos.MAX_COL), 'V')
+      local lines = range:lines()
+      assert.are.same({ 'line one' }, lines)
+
+      local text = range:text()
+      assert.are.same('line one', text)
+    end)
+  end)
+
+  it('get from positions: V across multiple lines', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.new(Pos.new(nil, 1, 0), Pos.new(nil, 2, Pos.MAX_COL), 'V')
+      local lines = range:lines()
+      assert.are.same({ 'the quick brown fox', 'jumps over a lazy dog' }, lines)
+    end)
+  end)
+
+  it('get from line', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.from_line(nil, 0)
+      local lines = range:lines()
+      assert.are.same({ 'line one' }, lines)
+
+      local text = range:text()
+      assert.are.same('line one', text)
+    end)
+  end)
+
+  it('get from lines', function()
+    withbuf({ 'line one', 'and line two', 'and line 3' }, function()
+      local range = Range.from_lines(nil, 0, 1)
+      local lines = range:lines()
+      assert.are.same({ 'line one', 'and line two' }, lines)
+
+      local text = range:text()
+      assert.are.same('line one\nand line two', text)
+    end)
+  end)
+
+  it('replace within line', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 1, 8), 'v')
+      range:replace 'quack'
+
+      local text = Range.from_line(nil, 1):text()
+      assert.are.same('the quack brown fox', text)
+    end)
+  end)
+
+  it('delete within line', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 1, 9), 'v')
+      range:replace ''
+
+      local text = Range.from_line(nil, 1):text()
+      assert.are.same('the brown fox', text)
+    end)
+
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 1, 9), 'v')
+      range:replace(nil)
+
+      local text = Range.from_line(nil, 1):text()
+      assert.are.same('the brown fox', text)
+    end)
+  end)
+
+  it('replace across multiple lines: v', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.new(Pos.new(nil, 1, 4), Pos.new(nil, 2, 4), 'v')
+      range:replace 'plane flew'
+
+      local lines = Range.from_buf_text():lines()
+      assert.are.same({
+        'pre line',
+        'the plane flew over a lazy dog',
+        'post line',
+      }, lines)
+    end)
+  end)
+
+  it('replace a line', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.from_line(nil, 1)
+      range:replace 'the rabbit'
+
+      local lines = Range.from_buf_text():lines()
+      assert.are.same({
+        'pre line',
+        'the rabbit',
+        'jumps over a lazy dog',
+        'post line',
+      }, lines)
+    end)
+  end)
+
+  it('replace multiple lines', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.from_lines(nil, 1, 2)
+      range:replace 'the rabbit'
+
+      local lines = Range.from_buf_text():lines()
+      assert.are.same({
+        'pre line',
+        'the rabbit',
+        'post line',
+      }, lines)
+    end)
+  end)
+
+  it('delete single line', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.from_line(nil, 1)
+      range:replace(nil) -- delete lines
+
+      local lines = Range.from_buf_text():lines()
+      assert.are.same({
+        'pre line',
+        'jumps over a lazy dog',
+        'post line',
+      }, lines)
+    end)
+  end)
+
+  it('delete multiple lines', function()
+    withbuf({ 'pre line', 'the quick brown fox', 'jumps over a lazy dog', 'post line' }, function()
+      local range = Range.from_lines(nil, 1, 2)
+      range:replace(nil) -- delete lines
+
+      local lines = Range.from_buf_text():lines()
+      assert.are.same({
+        'pre line',
+        'post line',
+      }, lines)
+    end)
+  end)
+
+  it('text object: word', function()
+    withbuf({ 'the quick brown fox' }, function()
+      vim.fn.setpos('.', { 0, 1, 5, 0 })
+      assert.are.same('quick ', Range.from_text_object('aw'):text())
+
+      vim.fn.setpos('.', { 0, 1, 5, 0 })
+      assert.are.same('quick', Range.from_text_object('iw'):text())
+    end)
+  end)
+
+  it('text object: quote', function()
+    withbuf({ [[the "quick" brown fox]] }, function()
+      vim.fn.setpos('.', { 0, 1, 5, 0 })
+      assert.are.same('"quick"', Range.from_text_object('a"'):text())
+
+      vim.fn.setpos('.', { 0, 1, 6, 0 })
+      assert.are.same('quick', Range.from_text_object('i"'):text())
+    end)
+
+    withbuf({ [[the 'quick' brown fox]] }, function()
+      vim.fn.setpos('.', { 0, 1, 5, 0 })
+      assert.are.same("'quick'", Range.from_text_object([[a']]):text())
+
+      vim.fn.setpos('.', { 0, 1, 6, 0 })
+      assert.are.same('quick', Range.from_text_object([[i']]):text())
+    end)
+
+    withbuf({ [[the `quick` brown fox]] }, function()
+      vim.fn.setpos('.', { 0, 1, 5, 0 })
+      assert.are.same('`quick`', Range.from_text_object([[a`]]):text())
+
+      vim.fn.setpos('.', { 0, 1, 6, 0 })
+      assert.are.same('quick', Range.from_text_object([[i`]]):text())
+    end)
+  end)
+
+  it('text object: block', function()
+    withbuf({ 'this is a {', 'block', '} here' }, function()
+      vim.fn.setpos('.', { 0, 2, 1, 0 })
+      assert.are.same('{\nblock\n}', Range.from_text_object('a{'):text())
+
+      vim.fn.setpos('.', { 0, 2, 1, 0 })
+      assert.are.same('block', Range.from_text_object('i{'):text())
+    end)
+  end)
+
+  it('text object: restores cursor position', function()
+    withbuf({ 'this is a {block} here' }, function()
+      vim.fn.setpos('.', { 0, 1, 13, 0 })
+      assert.are.same('{block}', Range.from_text_object('a{'):text())
+      assert.are.same(vim.api.nvim_win_get_cursor(0), { 1, 12 })
+    end)
+  end)
+
+  it('should get nearest block', function()
+    withbuf({
+      'this is a {',
+      'block',
+      '} here',
+    }, function()
+      vim.fn.setpos('.', { 0, 2, 1, 0 })
+      assert.are.same('{\nblock\n}', Range.find_nearest_brackets():text())
+    end)
+
+    withbuf({
+      'this is a {',
+      '(block)',
+      '} here',
+    }, function()
+      vim.fn.setpos('.', { 0, 2, 3, 0 })
+      assert.are.same('(block)', Range.find_nearest_brackets():text())
+    end)
+  end)
+
+  it('line0', function()
+    withbuf({
+      'this is a {',
+      'block',
+      '} here',
+    }, function()
+      local range = Range.new(Pos.new(0, 0, 5), Pos.new(0, 1, 4), 'v')
+      local lfirst = range:line0(0)
+      assert.are.same(5, lfirst.idx0.start)
+      assert.are.same(10, lfirst.idx0.stop)
+      assert.are.same(0, lfirst.lnum)
+      assert.are.same('is a {', lfirst.text())
+      assert.are.same('is a {', lfirst.range():text())
+      assert.are.same(Pos.new(0, 0, 5), lfirst.range().start)
+      assert.are.same(Pos.new(0, 0, 10), lfirst.range().stop)
+      assert.are.same('block', range:line0(1).text())
+    end)
+  end)
+
+  it('from_marks', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local a = Pos.new(nil, 0, 0)
+      local b = Pos.new(nil, 1, 1)
+      a:save_to_pos "'["
+      b:save_to_pos "']"
+
+      local range = Range.from_marks("'[", "']")
+      assert.are.same(range.start, a)
+      assert.are.same(range.stop, b)
+      assert.are.same(range.mode, 'v')
+    end)
+  end)
+
+  it('from_vtext', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      vim.fn.setpos('.', { 0, 1, 3, 0 }) -- cursor at position (1, 3)
+      vim.cmd.normal 'v' -- enter visual mode
+      vim.cmd.normal 'l' -- select one character to the right
+      local range = Range.from_vtext()
+      assert.are.same(range.start, Pos.new(nil, 0, 2))
+      assert.are.same(range.stop, Pos.new(nil, 0, 3))
+      assert.are.same(range.mode, 'v')
+    end)
+  end)
+
+  it('from_op_func', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local a = Pos.new(nil, 0, 0)
+      local b = Pos.new(nil, 1, 1)
+      a:save_to_pos "'["
+      b:save_to_pos "']"
+
+      local range = Range.from_op_func 'char'
+      assert.are.same(range.start, a)
+      assert.are.same(range.stop, b)
+      assert.are.same(range.mode, 'v')
+
+      range = Range.from_op_func 'line'
+      assert.are.same(range.start, a)
+      assert.are.same(range.stop, Pos.new(nil, 1, Pos.MAX_COL))
+      assert.are.same(range.mode, 'V')
+    end)
+  end)
+
+  it('from_cmd_args', function()
+    local args = { range = 1 }
+    withbuf({ 'line one', 'and line two' }, function()
+      local a = Pos.new(nil, 0, 0)
+      local b = Pos.new(nil, 1, 1)
+      a:save_to_pos "'<"
+      b:save_to_pos "'>"
+
+      local range = Range.from_cmd_args(args)
+      assert.are.same(range.start, a)
+      assert.are.same(range.stop, b)
+      assert.are.same(range.mode, 'v')
+    end)
+  end)
+
+  it('find_nearest_quotes', function()
+    withbuf({ [[the "quick" brown fox]] }, function()
+      vim.fn.setpos('.', { 0, 1, 5, 0 })
+      local range = Range.find_nearest_quotes()
+      assert.are.same(range.start, Pos.new(nil, 0, 4))
+      assert.are.same(range.stop, Pos.new(nil, 0, 10))
+    end)
+
+    withbuf({ [[the 'quick' brown fox]] }, function()
+      vim.fn.setpos('.', { 0, 1, 5, 0 })
+      local range = Range.find_nearest_quotes()
+      assert.are.same(range.start, Pos.new(nil, 0, 4))
+      assert.are.same(range.stop, Pos.new(nil, 0, 10))
+    end)
+  end)
+
+  it('smallest', function()
+    local r1 = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 0, 3), 'v')
+    local r2 = Range.new(Pos.new(nil, 0, 2), Pos.new(nil, 0, 4), 'v')
+    local r3 = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 5), 'v')
+    local smallest = Range.smallest { r1, r2, r3 }
+    assert.are.same(smallest.start, Pos.new(nil, 0, 1))
+    assert.are.same(smallest.stop, Pos.new(nil, 0, 3))
+  end)
+
+  it('clone', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local original = Range.from_lines(nil, 0, 1)
+      local cloned = original:clone()
+      assert.are.same(original.start, cloned.start)
+      assert.are.same(original.stop, cloned.stop)
+      assert.are.same(original.mode, cloned.mode)
+    end)
+  end)
+
+  it('line_count', function()
+    withbuf({ 'line one', 'and line two', 'line three' }, function()
+      local range = Range.from_lines(nil, 0, 2)
+      assert.are.same(range:line_count(), 3)
+    end)
+  end)
+
+  it('to_linewise()', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 1, 3), 'v')
+      local linewise_range = range:to_linewise()
+      assert.are.same(linewise_range.start.col, 0)
+      assert.are.same(linewise_range.stop.col, Pos.MAX_COL)
+      assert.are.same(linewise_range.mode, 'V')
+    end)
+  end)
+
+  it('is_empty', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 0), nil, 'v')
+      assert.is_true(range:is_empty())
+
+      local range2 = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 1), 'v')
+      assert.is_false(range2:is_empty())
+    end)
+  end)
+
+  it('trim_start', function()
+    withbuf({ '   line one', 'line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 9), 'v')
+      local trimmed = range:trim_start()
+      assert.are.same(trimmed.start, Pos.new(nil, 0, 3)) -- should be after the spaces
+    end)
+  end)
+
+  it('trim_stop', function()
+    withbuf({ 'line one   ', 'line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 0), Pos.new(nil, 0, 9), 'v')
+      local trimmed = range:trim_stop()
+      assert.are.same(trimmed.stop, Pos.new(nil, 0, 7)) -- should be before the spaces
+    end)
+  end)
+
+  it('contains', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 0, 3), 'v')
+      local pos = Pos.new(nil, 0, 2)
+      assert.is_true(range:contains(pos))
+
+      pos = Pos.new(nil, 0, 4) -- outside of range
+      assert.is_false(range:contains(pos))
+    end)
+  end)
+
+  it('shrink', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 1, 3), 'v')
+      local shrunk = range:shrink(1)
+      assert.are.same(shrunk.start, Pos.new(nil, 0, 2))
+      assert.are.same(shrunk.stop, Pos.new(nil, 1, 2))
+    end)
+  end)
+
+  it('must_shrink', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.new(Pos.new(nil, 0, 1), Pos.new(nil, 1, 3), 'v')
+      local shrunk = range:must_shrink(1)
+      assert.are.same(shrunk.start, Pos.new(nil, 0, 2))
+      assert.are.same(shrunk.stop, Pos.new(nil, 1, 2))
+
+      assert.has.error(function() range:must_shrink(100) end, 'error in Range:must_shrink: Range:shrink() returned nil')
+    end)
+  end)
+
+  it('set_visual_selection', function()
+    withbuf({ 'line one', 'and line two' }, function()
+      local range = Range.from_lines(nil, 0, 1)
+      range:set_visual_selection()
+
+      assert.are.same(Pos.from_pos 'v', Pos.new(nil, 0, 0))
+      assert.are.same(Pos.from_pos '.', Pos.new(nil, 1, 11))
+    end)
+  end)
+
+  it('selections set to past the EOL should not error', function()
+    withbuf({ 'Rg SET NAMES' }, function()
+      local b = vim.api.nvim_get_current_buf()
+      local r = Range.new(Pos.new(b, 0, 3), Pos.new(b, 0, 12), 'v')
+      r:replace 'bleh'
+      assert.are.same({ 'Rg bleh' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+    end)
+
+    withbuf({ 'Rg SET NAMES' }, function()
+      local b = vim.api.nvim_get_current_buf()
+      local r = Range.new(Pos.new(b, 0, 3), Pos.new(b, 0, 11), 'v')
+      r:replace 'bleh'
+      assert.are.same({ 'Rg bleh' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+    end)
+  end)
+
+  it('replace updates Range.stop: same line', function()
+    withbuf({ 'The quick brown fox jumps over the lazy dog' }, function()
+      local b = vim.api.nvim_get_current_buf()
+      local r = Range.new(Pos.new(b, 0, 4), Pos.new(b, 0, 8), 'v')
+
+      r:replace 'bleh1'
+      assert.are.same({ 'The bleh1 brown fox jumps over the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+
+      r:replace 'bleh2'
+      assert.are.same({ 'The bleh2 brown fox jumps over the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+    end)
+  end)
+
+  it('replace updates Range.stop: multi-line', function()
+    withbuf({
+      'The quick brown fox jumps',
+      'over the lazy dog',
+    }, function()
+      local b = vim.api.nvim_get_current_buf()
+      local r = Range.new(Pos.new(b, 0, 20), Pos.new(b, 1, 3), 'v')
+      assert.are.same({ 'jumps', 'over' }, r:lines())
+
+      r:replace 'bleh1'
+      assert.are.same({ 'The quick brown fox bleh1 the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+
+      r:replace 'blehGoo2'
+      assert.are.same({ 'The quick brown fox blehGoo2 the lazy dog' }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+    end)
+  end)
+
+  it('replace updates Range.stop: multi-line (blockwise)', function()
+    withbuf({
+      'The quick brown',
+      'fox',
+      'jumps',
+      'over',
+      'the lazy dog',
+    }, function()
+      local b = vim.api.nvim_get_current_buf()
+      local r = Range.new(Pos.new(b, 1, 0), Pos.new(b, 3, Pos.MAX_COL), 'V')
+      assert.are.same({ 'fox', 'jumps', 'over' }, r:lines())
+
+      r:replace { 'bleh1', 'bleh2' }
+      assert.are.same({
+        'The quick brown',
+        'bleh1',
+        'bleh2',
+        'the lazy dog',
+      }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+
+      r:replace 'blehGoo2'
+      assert.are.same({
+        'The quick brown',
+        'blehGoo2',
+        'the lazy dog',
+      }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+    end)
+  end)
+
+  it('replace after delete', function()
+    withbuf({
+      'The quick brown',
+      'fox',
+      'jumps',
+      'over',
+      'the lazy dog',
+    }, function()
+      local b = vim.api.nvim_get_current_buf()
+      local r = Range.new(Pos.new(b, 1, 0), Pos.new(b, 3, Pos.MAX_COL), 'V')
+      assert.are.same({ 'fox', 'jumps', 'over' }, r:lines())
+
+      r:replace(nil)
+      assert.are.same({
+        'The quick brown',
+        'the lazy dog',
+      }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+
+      r:replace { 'blehGoo2', '' }
+      assert.are.same({
+        'The quick brown',
+        'blehGoo2',
+        'the lazy dog',
+      }, vim.api.nvim_buf_get_lines(b, 0, -1, false))
+    end)
+  end)
+end)

spec/tracker_spec.lua

@@ -0,0 +1,206 @@
+local tracker = require 'u.tracker'
+local Signal = tracker.Signal
+local ExecutionContext = tracker.ExecutionContext
+
+describe('Signal', function()
+  local signal
+
+  before_each(function() signal = Signal:new(0, 'testSignal') end)
+
+  it('should initialize with correct parameters', function()
+    assert.is.equal(signal.value, 0)
+    assert.is.equal(signal.name, 'testSignal')
+    assert.is.not_nil(signal.subscribers)
+    assert.is.equal(#signal.subscribers, 0)
+    assert.is.equal(signal.changing, false)
+  end)
+
+  it('should set new value and notify subscribers', function()
+    local called = false
+    signal:subscribe(function(value)
+      called = true
+      assert.is.equal(value, 42)
+    end)
+
+    signal:set(42)
+    assert.is.equal(called, true)
+  end)
+
+  it('should not notify subscribers during circular dependency', function()
+    signal.changing = true
+    local notified = false
+
+    signal:subscribe(function() notified = true end)
+
+    signal:set(42)
+    assert.is.equal(notified, false) -- No notification should occur
+  end)
+
+  it('should get current value', function()
+    signal:set(100)
+    assert.is.equal(signal:get(), 100)
+  end)
+
+  it('should update value with function', function()
+    signal:set(10)
+    signal:update(function(value) return value * 2 end)
+    assert.is.equal(signal:get(), 20)
+  end)
+
+  it('should dispose subscribers', function()
+    local called = false
+    local unsubscribe = signal:subscribe(function() called = true end)
+
+    unsubscribe()
+    signal:set(10)
+    assert.is.equal(called, false) -- Should not be notified
+  end)
+
+  describe('Signal:map', function()
+    it('should transform the signal value', function()
+      local signal = Signal:new(5)
+      local mapped_signal = signal:map(function(value) return value * 2 end)
+
+      assert.is.equal(mapped_signal:get(), 10) -- Initial transformation
+      signal:set(10)
+      assert.is.equal(mapped_signal:get(), 20) -- Updated transformation
+    end)
+
+    it('should handle empty transformations', function()
+      local signal = Signal:new(nil)
+      local mapped_signal = signal:map(function(value) return value or 'default' end)
+
+      assert.is.equal(mapped_signal:get(), 'default') -- Return default
+      signal:set 'new value'
+      assert.is.equal(mapped_signal:get(), 'new value') -- Return new value
+    end)
+  end)
+
+  describe('Signal:filter', function()
+    it('should only emit values that pass the filter', function()
+      local signal = Signal:new(5)
+      local filtered_signal = signal:filter(function(value) return value > 10 end)
+
+      assert.is.equal(filtered_signal:get(), nil) -- Initial value should not pass
+      signal:set(15)
+      assert.is.equal(filtered_signal:get(), 15) -- Now filtered
+      signal:set(8)
+      assert.is.equal(filtered_signal:get(), 15) -- Does not pass the filter
+    end)
+
+    it('should handle empty initial values', function()
+      local signal = Signal:new(nil)
+      local filtered_signal = signal:filter(function(value) return value ~= nil end)
+
+      assert.is.equal(filtered_signal:get(), nil) -- Should be nil
+      signal:set(10)
+      assert.is.equal(filtered_signal:get(), 10) -- Should pass now
+    end)
+  end)
+
+  describe('create_memo', function()
+    it('should compute a derived value and update when dependencies change', function()
+      local signal = Signal:new(2)
+      local memoized_signal = tracker.create_memo(function() return signal:get() * 2 end)
+
+      assert.is.equal(memoized_signal:get(), 4) -- Initially compute 2 * 2
+
+      signal:set(3)
+      assert.is.equal(memoized_signal:get(), 6) -- Update to 3 * 2 = 6
+
+      signal:set(5)
+      assert.is.equal(memoized_signal:get(), 10) -- Update to 5 * 2 = 10
+    end)
+
+    it('should not recompute if the dependencies do not change', function()
+      local call_count = 0
+      local signal = Signal:new(10)
+      local memoized_signal = tracker.create_memo(function()
+        call_count = call_count + 1
+        return signal:get() + 1
+      end)
+
+      assert.is.equal(memoized_signal:get(), 11) -- Compute first value
+      assert.is.equal(call_count, 1) -- Should compute once
+
+      memoized_signal:get() -- Call again, should use memoized value
+      assert.is.equal(call_count, 1) -- Still should only be one call
+
+      signal:set(10) -- Set the same value
+      assert.is.equal(memoized_signal:get(), 11)
+      assert.is.equal(call_count, 2)
+
+      signal:set(20)
+      assert.is.equal(memoized_signal:get(), 21)
+      assert.is.equal(call_count, 3)
+    end)
+  end)
+
+  describe('create_effect', function()
+    it('should track changes and execute callback', function()
+      local signal = Signal:new(5)
+      local call_count = 0
+
+      tracker.create_effect(function()
+        signal:get() -- track as a dependency
+        call_count = call_count + 1
+      end)
+
+      assert.is.equal(call_count, 1)
+      signal:set(10)
+      assert.is.equal(call_count, 2)
+    end)
+
+    it('should clean up signals and not call after dispose', function()
+      local signal = Signal:new(5)
+      local call_count = 0
+
+      local unsubscribe = tracker.create_effect(function()
+        call_count = call_count + 1
+        return signal:get() * 2
+      end)
+
+      assert.is.equal(call_count, 1) -- Initially calls
+      unsubscribe() -- Unsubscribe the effect
+      signal:set(10) -- Update signal value
+      assert.is.equal(call_count, 1) -- Callback should not be called again
+    end)
+  end)
+end)
+
+describe('ExecutionContext', function()
+  local context
+
+  before_each(function() context = ExecutionContext:new() end)
+
+  it('should initialize a new context', function()
+    assert.is.table(context.signals)
+    assert.is.table(context.subscribers)
+  end)
+
+  it('should track signals', function()
+    local signal = Signal:new(0)
+    context:track(signal)
+
+    assert.is.equal(next(context.signals), signal) -- Check if signal is tracked
+  end)
+
+  it('should subscribe to signals', function()
+    local signal = Signal:new(0)
+    local callback_called = false
+
+    context:track(signal)
+    context:subscribe(function() callback_called = true end)
+
+    signal:set(100)
+    assert.is.equal(callback_called, true) -- Callback should be called
+  end)
+
+  it('should dispose tracked signals', function()
+    local signal = Signal:new(0)
+    context:track(signal)
+
+    context:dispose()
+    assert.is.falsy(next(context.signals)) -- Should not have any tracked signals
+  end)
+end)

spec/utils_spec.lua

@@ -0,0 +1,70 @@
+local utils = require 'u.utils'
+
+--- @param s string
+local function split(s) return vim.split(s, '') end
+
+--- @param original string
+--- @param changes LevenshteinChange[]
+local function morph(original, changes)
+  local t = split(original)
+  for _, change in ipairs(changes) do
+    if change.kind == 'add' then
+      table.insert(t, change.index, change.item)
+    elseif change.kind == 'delete' then
+      table.remove(t, change.index)
+    elseif change.kind == 'change' then
+      t[change.index] = change.to
+    end
+  end
+  return vim.iter(t):join ''
+end
+
+describe('utils', function()
+  it('levenshtein', function()
+    local original = 'abc'
+    local result = 'absece'
+    local changes = utils.levenshtein(split(original), split(result))
+    assert.are.same(changes, {
+      {
+        item = 'e',
+        kind = 'add',
+        index = 4,
+      },
+      {
+        item = 'e',
+        kind = 'add',
+        index = 3,
+      },
+      {
+        item = 's',
+        kind = 'add',
+        index = 3,
+      },
+    })
+    assert.are.same(morph(original, changes), result)
+
+    original = 'jonathan'
+    result = 'ajoanthan'
+    changes = utils.levenshtein(split(original), split(result))
+    assert.are.same(changes, {
+      {
+        from = 'a',
+        index = 4,
+        kind = 'change',
+        to = 'n',
+      },
+      {
+        from = 'n',
+        index = 3,
+        kind = 'change',
+        to = 'a',
+      },
+      {
+        index = 1,
+        item = 'a',
+        kind = 'add',
+      },
+    })
+    assert.are.same(morph(original, changes), result)
+  end)
+end)

spec/withbuf.lua

@@ -0,0 +1,10 @@
+local function withbuf(lines, f)
+  vim.opt_global.swapfile = false
+
+  vim.cmd.new()
+  vim.api.nvim_buf_set_lines(0, 0, -1, false, lines)
+  local ok, result = pcall(f)
+  vim.cmd.bdelete { bang = true }
+  if not ok then error(result) end
+end
+return withbuf

stylua.toml

@@ -1,10 +1,6 @@
-syntax = "LuaJIT"
 call_parentheses = "None"
 collapse_simple_statement = "Always"
-column_width = 100
+column_width = 120
 indent_type = "Spaces"
 indent_width = 2
 quote_style = "AutoPreferSingle"
-
-[sort_requires]
-enabled = true

u-0.0.0-0.rockspec

@@ -1,16 +0,0 @@
-rockspec_format = '3.0'
-package = 'u'
-version = '0.0.0-0'
-
-source = {
-  url = 'https://github.com/jrop/u.nvim',
-}
-
-dependencies = {
-  'lua = 5.1',
-}
-
-test_dependencies = {
-  'busted == 2.2.0-1',
-  'luacov == 0.16.0-1',
-}

u.nvim-0.2.0-1.rockspec

@@ -0,0 +1,24 @@
+package = "u.nvim"
+version = "0.2.0-1"
+source = {
+   url = "git+https://github.com/jrop/u.nvim"
+}
+description = {
+   summary = "nvim – a powerful Lua library designed to enhance your text manipulation experience in NeoVim, focusing primarily on a context-aware \"Range\" utility.",
+   detailed = "Welcome to u.nvim – a powerful Lua library designed to enhance your text manipulation experience in NeoVim, focusing primarily on a context-aware \"Range\" utility. This utility allows you to work efficiently with text selections based on various conditions, in a variety of contexts, making coding and editing more intuitive and productive.",
+   homepage = "https://github.com/jrop/u.nvim",
+   license = "MIT"
+}
+build = {
+   type = "builtin",
+   modules = {
+      ["u.buffer"] = "lua/u/buffer.lua",
+      ["u.codewriter"] = "lua/u/codewriter.lua",
+      ["u.opkeymap"] = "lua/u/opkeymap.lua",
+      ["u.pos"] = "lua/u/pos.lua",
+      ["u.range"] = "lua/u/range.lua",
+      ["u.repeat"] = "lua/u/repeat.lua",
+      ["u.state"] = "lua/u/state.lua",
+      ["u.utils"] = "lua/u/utils.lua"
+   }
+}

vim.yml

@@ -0,0 +1,36 @@
+---
+base: lua51
+globals:
+  vim:
+    any: true
+  assert.are.same:
+    args:
+      - type: any
+      - type: any
+  assert.are_not.same:
+    args:
+      - type: any
+      - type: any
+  assert.has.error:
+    args:
+      - type: any
+      - type: any
+  assert.is_true:
+    args:
+      - type: any
+      - type: any
+  assert.is_false:
+    args:
+      - type: any
+      - type: any
+  describe:
+    args:
+      - type: string
+      - type: function
+  it:
+    args:
+      - type: string
+      - type: function
+  before_each:
+    args:
+      - type: function