very basic saving (hardcoded file name, which is fine fow now)

imperative-shell/file-thread.sml

@@ -5,14 +5,50 @@ end
 
 structure FileThread :> FILE_THREAD =
 struct
+  open AppType
   open FileMessage
 
+  val filename = "a.dsc"
+
+  fun helpSaveTriangles (triangles, io) =
+    case triangles of
+      {x1, y1, x2, y2, x3, y3} :: tl =>
+        let
+          val triString = String.concat
+            [ "x1:"
+            , Real32.toString x1
+            , " y1:"
+            , Real32.toString y1
+
+            , " x2:"
+            , Real32.toString x2
+            , " y2:"
+            , Real32.toString y2
+
+            , " x3:"
+            , Real32.toString x3
+            , " y3:"
+            , Real32.toString y3
+            , "\n"
+            ]
+
+          val _ = TextIO.output (io, triString)
+        in
+          helpSaveTriangles (tl, io)
+        end
+    | [] => ()
+
+  fun saveTriangles triangles =
+    let val io = TextIO.openOut filename
+    in helpSaveTriangles (triangles, io)
+    end
+
   fun run fileMailbox =
     let
       val _ =
         case Mailbox.recv fileMailbox of
-          SAVE_TRIANGLES triangles => ()
-        | LOAD_TRIANGLES triangles => ()
+          SAVE_TRIANGLES triangles => saveTriangles triangles
+        | LOAD_TRIANGLES => ()
         | EXPORT_TRIANGLES triangles => ()
     in
       run fileMailbox