create constant vector that looks like graph paper (grid for clicking points later)

functional-core/app-type.sml

@@ -0,0 +1,42 @@
+structure AppType =
+struct
+  type triangle =
+    { x1: Real32.real
+    , y1: Real32.real
+    , x2: Real32.real
+    , y2: Real32.real
+    , x3: Real32.real
+    , y3: Real32.real
+    }
+
+  datatype triangle_stage =
+    NO_TRIANGLE
+  (* 
+   * triangle_stage represents a work-in-progress triangle which is not fully completed,
+   * because user has to click one (x, y) pair, then a second pair, 
+   * and then a third, to draw a complete triangle.
+   *
+   * There is no THIRD triangle_stage because that represents a complete triangle, 
+   * which should be added to the `triangles` list. 
+   *)
+  | FIRST of {x1: Real32.real, y1: Real32.real}
+  | SECOND of
+      {x1: Real32.real, y1: Real32.real, x2: Real32.real, y2: Real32.real}
+
+  type app_type = {triangles: triangle list, triangleStage: triangle_stage}
+
+  local
+    fun helpGetTrianglesVector (lst, acc) =
+      case lst of
+        {x1, y1, x2, y2, x3, y3} :: tl =>
+          let val vec = Vector.fromList [x1, y1, x2, y2, x3, y3]
+          in helpGetTrianglesVector (tl, vec :: acc)
+          end
+      | [] => acc
+  in
+    fun getTrianglesVector (app: app_type) =
+      let val lst = helpGetTrianglseVector (#triangles app, [])
+      in Vector.concat lst
+      end
+  end
+end