diff --git a/dot-to-dot b/dot-to-dot
index ba4ff47..80fcfa4 100755
Binary files a/dot-to-dot and b/dot-to-dot differ
diff --git a/dot-to-dot.mlb b/dot-to-dot.mlb
index 89bb2e5..81ab1a7 100644
--- a/dot-to-dot.mlb
+++ b/dot-to-dot.mlb
@@ -10,8 +10,9 @@ in
   ffi/glfw-input.sml
 end
 
+message-types/input-msg.sml
+
 functional-core/app-type.sml
-functional-core/msg.sml
 functional-core/app-update.sml
 
 ann
diff --git a/functional-core/app-update.sml b/functional-core/app-update.sml
index 365cecd..2f42ee4 100644
--- a/functional-core/app-update.sml
+++ b/functional-core/app-update.sml
@@ -1 +1,75 @@
-structure AppUpdate = struct end
+structure AppUpdate =
+struct
+  val clickPoints =
+   #[ 25
+    , 50
+    , 75
+    , 100
+    , 125
+    , 150
+    , 175
+    , 200
+    , 225
+    , 250
+    , 275
+    , 300
+    , 325
+    , 350
+    , 375
+    , 400
+    , 425
+    , 450
+    , 475
+    ]
+
+  local
+    fun getVerticalClickPos (idx, horizontalPos, mouseX, mouseY) =
+      if idx = Vector.length clickPoints then
+        #[]
+      else
+        let
+          val curVerticalPos = Vector.sub (clickPoints, idx)
+        in
+          if mouseY < curVerticalPos - 10 orelse mouseY > curVerticalPos + 10 then
+            getVerticalClickPos (idx + 1, horizontalPos, mouseX, mouseY)
+          else
+            let
+              val left = Real32.fromInt ((horizontalPos - 10) div 500)
+              val right = Real32.fromInt ((horizontalPos + 10) div 500)
+              val bottom = Real32.fromInt ((curVerticalPos - 10) div 500)
+              val top = Real32.fromInt ((curVerticalPos + 10) div 500)
+            in
+              val highlightSquare = #[
+                left, bottom, (* lower left *)
+                right, bottom, (* lower right *)
+                left, top, (* upper left *)
+
+                left, top, (* upper left *)
+                right, bottom, (* lower right *)
+                right, top (* upper right *)
+              ]
+            end
+        end
+
+    fun getHorizontalClickPos (idx, mouseX, mouseY) =
+      if idx = Vector.length clickPoints then
+        #[]
+      else
+        let
+          val curPos = Vector.sub (clickPoints, idx)
+        in
+          if mouseX < curPos - 10 orelse mouseX > curPos + 10 then
+            getHorizontalClickPos (idx + 1, mouseX, mouseY)
+          else
+            getVerticalClickPos (0, curPos, mouseX, mouseY)
+        end
+  in
+    (*
+     * This function returns a vector containing the position data of the
+     * clicked square.
+     * If a square wasn't found at the clicked position, 
+     * an empty vector is returned.
+     *)
+    fun getClickPos (mouseX, mouseY) = getHorizontalClickPos (0, mouseX, mouseY)
+  end
+end
diff --git a/imperative-shell/input-callbacks.sml b/imperative-shell/input-callbacks.sml
index 99eb570..252560d 100644
--- a/imperative-shell/input-callbacks.sml
+++ b/imperative-shell/input-callbacks.sml
@@ -1,7 +1,7 @@
 structure InputCallbacks =
 struct
   open CML
-  open Msg
+  open InputMessage
 
   fun mouseMoveCallback mailbox (x, y) =
     Mailbox.send (mailbox, (MOUSE_MOVE {x = x, y = y}))
diff --git a/imperative-shell/shell.sml b/imperative-shell/shell.sml
index 225fba3..2370f0e 100644
--- a/imperative-shell/shell.sml
+++ b/imperative-shell/shell.sml
@@ -4,7 +4,7 @@ struct
 
   fun callbackListener mailbox =
     let
-      open Msg
+      open InputMessage
       val _ =
         case Mailbox.recv mailbox of
           MOUSE_MOVE {x, y} =>
diff --git a/message-types/draw-msg.sml b/message-types/draw-msg.sml
new file mode 100644
index 0000000..d6adc1e
--- /dev/null
+++ b/message-types/draw-msg.sml
@@ -0,0 +1,9 @@
+signature DRAW_MESSAGE =
+sig
+
+end
+
+structure DrawMessage :> DRAW_MESSAGE =
+struct
+
+end
diff --git a/functional-core/msg.sml b/message-types/input-msg.sml
similarity index 75%
rename from functional-core/msg.sml
rename to message-types/input-msg.sml
index 9eb30a7..d15c69f 100644
--- a/functional-core/msg.sml
+++ b/message-types/input-msg.sml
@@ -1,4 +1,4 @@
-signature MSG =
+signature INPUT_MESSAGE =
 sig
   datatype t =
     MOUSE_MOVE of {x: int, y: int}
@@ -6,7 +6,7 @@ sig
   | MOUSE_LEFT_RELEASE
 end
 
-structure Msg :> MSG =
+structure InputMessage :> INPUT_MESSAGE =
 struct
   datatype t =
     MOUSE_MOVE of {x: int, y: int}