6811 - tile: left-cursor movement

Displayed cursor position is not yet correct, but insertions happen at
the right cursor position.

apps/tile/environment.mu

@@ -46,11 +46,26 @@ $process:body: {
     compare key, 0x445b1b  # left-arrow
     {
       break-if-!=
-      # TODO:
-      #   gap-left cursor-word
-      # or
-      #   cursor-word = cursor-word->prev
-      #   gap-to-end cursor-word
+      var cursor-word-ah/edi: (addr handle word) <- get self, cursor-word
+      var _cursor-word/eax: (addr word) <- lookup *cursor-word-ah
+      var cursor-word/ecx: (addr word) <- copy _cursor-word
+      # if not at start, gap-left
+      var at-start?/eax: boolean <- cursor-at-start? cursor-word
+      compare at-start?, 0  # false
+      {
+        break-if-=
+        cursor-left cursor-word
+        break $process:body
+      }
+      # otherwise, move gap to end of prev word
+      var prev-word-ah/esi: (addr handle word) <- get cursor-word, prev
+      var prev-word/eax: (addr word) <- lookup *prev-word-ah
+      {
+        compare prev-word, 0
+        break-if-=
+        copy-object prev-word-ah, cursor-word-ah
+        cursor-to-end prev-word
+      }
       break $process:body
     }
     compare key, 0x435b1b  # right-arrow

apps/tile/gap-buffer.mu

@@ -114,6 +114,18 @@ fn gap-to-end self: (addr gap-buffer) {
   }
 }
 
+fn gap-at-start? _self: (addr gap-buffer) -> result/eax: boolean {
+  var self/esi: (addr gap-buffer) <- copy _self
+  var left/eax: (addr grapheme-stack) <- get self, left
+  result <- grapheme-stack-empty? left
+}
+
+fn gap-at-end? _self: (addr gap-buffer) -> result/eax: boolean {
+  var self/esi: (addr gap-buffer) <- copy _self
+  var right/eax: (addr grapheme-stack) <- get self, right
+  result <- grapheme-stack-empty? right
+}
+
 fn gap-right _self: (addr gap-buffer) -> result/eax: grapheme {
 $gap-right:body: {
   var self/esi: (addr gap-buffer) <- copy _self

apps/tile/word.mu

@@ -98,6 +98,42 @@ fn add-grapheme-to-word _self: (addr word), c: grapheme {
   add-grapheme-at-gap data, c
 }
 
+fn cursor-at-start? _self: (addr word) -> result/eax: boolean {
+  var self/esi: (addr word) <- copy _self
+  var data/eax: (addr gap-buffer) <- get self, data
+  result <- gap-at-start? data
+}
+
+fn cursor-at-end? _self: (addr word) -> result/eax: boolean {
+  var self/esi: (addr word) <- copy _self
+  var data/eax: (addr gap-buffer) <- get self, data
+  result <- gap-at-end? data
+}
+
+fn cursor-left _self: (addr word) {
+  var self/esi: (addr word) <- copy _self
+  var data/eax: (addr gap-buffer) <- get self, data
+  var dummy/eax: grapheme <- gap-left data
+}
+
+fn cursor-right _self: (addr word) {
+  var self/esi: (addr word) <- copy _self
+  var data/eax: (addr gap-buffer) <- get self, data
+  var dummy/eax: grapheme <- gap-right data
+}
+
+fn cursor-to-start _self: (addr word) {
+  var self/esi: (addr word) <- copy _self
+  var data/eax: (addr gap-buffer) <- get self, data
+  gap-to-start data
+}
+
+fn cursor-to-end _self: (addr word) {
+  var self/esi: (addr word) <- copy _self
+  var data/eax: (addr gap-buffer) <- get self, data
+  gap-to-end data
+}
+
 fn print-word screen: (addr screen), _self: (addr word) {
   var self/esi: (addr word) <- copy _self
   var data/eax: (addr gap-buffer) <- get self, data