100/home/humza/Downloads/sml/dotscape/README.md done with undo/redo functionality (tested and both of them work as expected)

README.md

@@ -45,7 +45,7 @@ This isn't an exhaustive list, but these are some features I would like to add t
 
 - [x] Display clicked positions
 - [x] Redraw components when resized
-- [ ] Support undo (with `<Ctrl-z>`) and redo (with `<Ctrl-y>` or `<Ctrl-Shift-z>`)
+- [x] Support undo (with `<Ctrl-z>`) and redo (with `<Ctrl-y>` or `<Ctrl-Shift-z>`)
 - [ ] Export to code 
   - Possibly different options like creating a flat array/vector or an index buffer
 - [ ] Linear interpolation 

ffi/glfw-input.c

@@ -5,6 +5,7 @@ int PRESS = GLFW_PRESS;
 int RELEASE = GLFW_RELEASE;
 int LEFT_MOUSE_BUTTON = GLFW_MOUSE_BUTTON_1;
 int KEY_Z = GLFW_KEY_Z;
+int KEY_Y = GLFW_KEY_Y;
 
 // Calls function exported from SML 
 void mouseMoveCallback(GLFWwindow *window, double xpos, double ypos) {

ffi/glfw-input.sml

@@ -33,4 +33,6 @@ struct
 
   val (KEY_Z, _) =
     _symbol "KEY_Z" public : ( unit -> int ) * ( int -> unit );
+  val (KEY_Y, _) =
+    _symbol "KEY_Y" public : ( unit -> int ) * ( int -> unit );
 end

imperative-shell/input-callbacks.sml

@@ -21,9 +21,24 @@ struct
   fun keyActionCallback mailbox (key, scancode, action, mods) =
     if
       key = Input.KEY_Z () andalso action <> Input.RELEASE ()
+    then
+      if mods = 0x0002 then
+        (* ctrl-z *)
+        Mailbox.send (mailbox, UNDO_ACTION)
+      else if mods = 0x0003 then
+        (* ctrl-shift-z *)
+        Mailbox.send (mailbox, REDO_ACTION)
+      else
+        (* no action recognised *)
+        ()
+    else if
+      key = Input.KEY_Y () andalso action <> Input.RELEASE ()
       andalso mods = 0x0002
-    then Mailbox.send (mailbox, UNDO_ACTION)
-    else ()
+    then
+      (* ctrl-y *)
+      Mailbox.send (mailbox, REDO_ACTION)
+    else
+      ()
 
   fun registerCallbacks (window, inputMailbox) =
     let