save grid to custom format

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)