additional scaffolding for making RGFW main loop

shell/rgfw-loop.sml

@@ -1,20 +1,51 @@
 structure RgfwLoop =
 struct
-  fun loop window =
+  fun loop (window, app) =
     if Rgfw.shouldCloseWindow window then
       Rgfw.closeWindow window
     else
-      let 
+      let
+        val _ = Gles3.clearColor (0.89, 0.89, 0.89, 1.0)
+        val _ = Gles3.clear ()
         val () = Rgfw.swapBuffers window
-      in 
-        loop window
+      in
+        loop (window, app)
       end
 
+  local
+    fun loop (io, acc, lastCharWasNewline) =
+      case TextIO.inputLine io of
+        SOME str =>
+          let
+            val endsWithNewline =
+              String.size str > 0
+              andalso String.sub (str, String.size str - 1) = #"\n"
+          in
+            loop (io, LineGap.append (str, acc), endsWithNewline)
+          end
+      | NONE =>
+          if lastCharWasNewline then
+            LineGap.goToStart acc
+          else
+            let val acc = LineGap.append ("\n", acc)
+            in LineGap.goToStart acc
+            end
+  in
+    fun ioToLineGap (io, acc) = loop (io, acc, false)
+  end
+
   fun main () =
     let
       val window = Rgfw.createWindow ("shf", 0, 0, 1920, 1080)
+      val () = Gles3.enableDepthTest ()
+
+      (* load file intol gap buffer and create initial app *)
+      val io = TextIO.openIn "temp.txt"
+      val lineGap = ioToLineGap (io, LineGap.empty)
+      val _ = TextIO.closeIn io
+      val app = AppType.init (lineGap, 1920, 1080, Time.now ())
     in
-      loop window
+      loop (window, app)
     end
 end