diff --git a/dotscape b/dotscape
index cb8b756..79f1b7c 100755
Binary files a/dotscape and b/dotscape differ
diff --git a/fcore/app-with.sml b/fcore/app-with.sml
index 462e71b..4738112 100644
--- a/fcore/app-with.sml
+++ b/fcore/app-with.sml
@@ -3,12 +3,12 @@ struct
   open AppType
 
   fun updateSquares (squares, newX, newY, item) =
-  let
-    val yAxis = Vector.sub (squares, newX)
-    val yAxis = Vector.update (yAxis, newY, item)
-  in
-    Vector.update (squares, newX, yAxis)
-  end
+    let
+      val yAxis = Vector.sub (squares, newX)
+      val yAxis = Vector.update (yAxis, newY, item)
+    in
+      Vector.update (squares, newX, yAxis)
+    end
 
   fun changeSquaresSize (squares, newCanvasWidth, newCanvasHeight) =
     let
diff --git a/fcore/common-update.sml b/fcore/common-update.sml
index f19cccd..7ece0d5 100644
--- a/fcore/common-update.sml
+++ b/fcore/common-update.sml
@@ -1,8 +1,22 @@
 structure CommonUpdate =
 struct
-  (* unimplemented *)
-  fun getSaveSquaresMsg model = (model, [])
+  open AppType
 
+  open DrawMessage
+  open FileMessage
+  open InputMessage
+  open UpdateMessage
+
+  fun getSaveSquaresMsg (model: app_type) =
+    let
+      val {canvasWidth, canvasHeight, squares, ...} = model
+      val str = CollisionTree.toString (squares, canvasWidth, canvasHeight)
+      val msg = SAVE_SQUARES str
+    in
+      (model, [FILE msg])
+    end
+
+  (* unimplemented *)
   fun getLoadSquaresMsg model = (model, [])
 
   fun getExportSquaresMsg model = (model, [])
diff --git a/fcore/quad-tree.sml b/fcore/quad-tree.sml
index de0e144..7076764 100644
--- a/fcore/quad-tree.sml
+++ b/fcore/quad-tree.sml
@@ -520,19 +520,25 @@ struct
         , Int.toString b
         , " "
         , Int.toString a
-        , " }"
+        , " } "
         ]
     in
       item :: acc
     end
 
-  fun toString (squares, size) =
+  fun toString (squares, canvasWidth, canvasHeight) =
     let
+      val size = Int.max (canvasWidth, canvasHeight)
       val qtree = buildTree (0, 0, size, squares)
       val bintree = merge (qtree, squares)
 
-      val vec = BinTree.foldr (toStringFolder, bintree, [])
+      val initial = ["}"]
+      val acc = BinTree.foldr (toStringFolder, bintree, initial)
+      val acc =
+        String.concat
+          [Int.toString canvasWidth, " ", Int.toString canvasHeight, " { "]
+        :: acc
     in
-      Vector.concat vec
+      String.concat acc
     end
 end
diff --git a/imperative-shell/file-thread.sml b/imperative-shell/file-thread.sml
index f130f01..078d7f4 100644
--- a/imperative-shell/file-thread.sml
+++ b/imperative-shell/file-thread.sml
@@ -51,7 +51,13 @@ struct
 
   fun loadSquares (path, inputMailbox) = ()
 
-  fun saveSquares squares = ()
+  fun saveSquares squaresString =
+    let
+      val io = TextIO.openOut filename
+      val () = TextIO.output (io, squaresString)
+    in
+      TextIO.closeOut io
+    end
 
   fun getDirList (dir, acc, rootPath) =
     case OS.FileSys.readDir dir of
@@ -87,7 +93,7 @@ struct
     let
       val _ =
         case Mailbox.recv fileMailbox of
-          SAVE_SQUARES triangles => saveSquares triangles
+          SAVE_SQUARES str => saveSquares str
         | LOAD_SQUARES => loadSquares (filename, inputMailbox)
         | EXPORT_SQUARES triangles => exportSquares triangles
         | LOAD_FILES path => loadFiles (path, inputMailbox)
diff --git a/message-types/file-msg.sml b/message-types/file-msg.sml
index 02156db..8a59384 100644
--- a/message-types/file-msg.sml
+++ b/message-types/file-msg.sml
@@ -1,7 +1,7 @@
 structure FileMessage =
 struct
   datatype t =
-    SAVE_SQUARES of int vector vector
+    SAVE_SQUARES of string
   | LOAD_SQUARES
   | EXPORT_SQUARES of int vector vector
   | LOAD_FILES of string