update lua API to 1-based indices; add renderer

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)