From cf896546d7ea6d8d5dfa4718b2a58ff87fcbb74c Mon Sep 17 00:00:00 2001
From: Jonathan Apodaca <jrapodaca@gmail.com>
Date: Sat, 14 Jun 2025 00:19:11 -0600
Subject: [PATCH] add example/form.lua

---
 examples/form.lua  | 43 +++++++++++++++++++++++++++++++++++++++++++
 lua/u/renderer.lua |  5 +++++
 2 files changed, 48 insertions(+)
 create mode 100644 examples/form.lua

diff --git a/examples/form.lua b/examples/form.lua
new file mode 100644
index 0000000..e02db52
--- /dev/null
+++ b/examples/form.lua
@@ -0,0 +1,43 @@
+local h = require('u.renderer').h
+local Renderer = require('u.renderer').Renderer
+local tracker = require 'u.tracker'
+
+-- Create a new, temporary, buffer to the side:
+vim.cmd.vnew()
+vim.bo.buftype = 'nofile'
+vim.bo.bufhidden = 'wipe'
+vim.bo.buflisted = false
+local renderer = Renderer.new()
+
+-- Create two signals:
+local s_name = tracker.create_signal '[(name here)]'
+local s_age = tracker.create_signal '[(age here)]'
+
+-- Utility to trim brackets from strings:
+local function trimb(s) return (s:gsub('^%[(.*)%]$', '%1')) end
+
+-- Render effect that depends on the signals. This will re-run every time
+-- one of the signals changes.
+tracker.create_effect(function()
+  local name = s_name:get()
+  local age = s_age:get()
+
+  -- Each time the signals change, we re-render the buffer:
+  renderer:render {
+    h.Type({}, '# Form Example'),
+    '\n\n',
+
+    -- Setting the `signal` attribute to a signal will cause the renderer to
+    -- update the signal's value whenever text in the tag is changed. This lets
+    -- us setup two-way data-binding between the buffer and the signals.
+    { 'Name: ', h.Structure({ signal = s_name }, name) },
+    '\n',
+    { 'Age: ', h.Structure({ signal = s_age }, age) },
+
+    '\n\n',
+
+    -- Display the current values of the signals. If you change the values in
+    -- the tags above, you can see the changes reflected here immediately.
+    { 'Hello, "', trimb(name), '", you are "', trimb(age), '" years old.' },
+  }
+end)
diff --git a/lua/u/renderer.lua b/lua/u/renderer.lua
index 8696be8..3c34f50 100644
--- a/lua/u/renderer.lua
+++ b/lua/u/renderer.lua
@@ -296,10 +296,15 @@ function Renderer:_reconcile() -- {{{
 
   --
   -- Step 2: reconcile extmarks:
+  -- You may be tempted to try to keep track of which extmarks are needed, and
+  -- only delete those that are not needed. However, each time a tree is
+  -- rendered, brand new extmarks are created. For simplicity, it is better to
+  -- just delete all extmarks, and recreate them.
   --
 
   -- 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(