implemented 'yh' motion (yank left)

fcore/normal-mode/normal-mode.sml

@@ -461,11 +461,8 @@ struct
 
     fun parseYankTerminal (str, count, app, chrCmd, time) =
       case chrCmd of
-      (* motions like yh / yj / yk / yl are not really needed.
-       * Vim supports them, but I never use them.
-       * I also don't need yx (yank a character and then remove it)
-       * because I never do that. *)
-        #"y" => NormalYank.yankLine (app, count)
+        #"h" => NormalYank.yankLeft (app, count)
+      | #"y" => NormalYank.yankLine (app, count)
       | #"0" => NormalYank.yankToStartOfLine app
       | #"w" => NormalYank.yankWhenMovingForward (app, Cursor.nextWord, count)
       | #"W" => NormalYank.yankWhenMovingForward (app, Cursor.nextWORD, count)

fcore/normal-mode/normal-yank.sml

@@ -4,6 +4,24 @@ struct
   open DrawMsg
   open MailboxType
 
+  fun yankLeft (app: app_type, count) =
+    let
+      val {buffer, cursorIdx, ...} = app
+
+      val buffer = LineGap.goToIdx (cursorIdx, buffer)
+      val min = Cursor.vi0 (buffer, cursorIdx)
+      val low = Cursor.viH (buffer, cursorIdx, 1)
+
+      val low = Int.max (min, low)
+      val length = cursorIdx - low
+      val str = LineGap.substring (low, length, buffer)
+
+      val msg = YANK str
+      val mode = NORMAL_MODE ""
+    in
+      NormalModeWith.modeAndBuffer (app, buffer, mode, [DRAW msg])
+    end
+
   fun yankLine (app: app_type, count) =
     let
       val {buffer, cursorIdx, ...} = app

todo.md

@@ -1,3 +1,4 @@
 # To-do list
 
-- Add yank commands like yh/yj/yk/yl as well and then add tests for yanking.
+- Implement `yh` motion.
+  - Implemented. Add tests for it next (based on tests for 'dh' motion).