add mode type to app type (equivalent of vi's normal mode, visual mode, insert mode, etc.)

fcore/app-type.sml

@@ -1,7 +1,30 @@
-structure AppType =
-struct
+signature APP_TYPE =
+sig
+  datatype mode = 
+    NORMAL_MODE of string
+
   type app_type =
-    { buffer: LineGap.t
+    { mode: mode
+    , buffer: LineGap.t
+    , windowWidth: int
+    , windowHeight: int
+    (* line to start drawing from *)
+    , startLine: int
+    (* absolute index of movable cursor *)
+    , cursorIdx: int
+    }
+
+  val init: LineGap.t * int * int -> app_type
+end
+
+structure AppType :> APP_TYPE =
+struct
+  datatype mode =
+    NORMAL_MODE of string
+
+  type app_type =
+    { mode: mode
+    , buffer: LineGap.t
     , windowWidth: int
     , windowHeight: int
     (* line to start drawing from *)
@@ -11,7 +34,8 @@ struct
     }
 
   fun init (buffer, windowWidth, windowHeight) : app_type =
-    { buffer = buffer
+    { mode = NORMAL_MODE ""
+    , buffer = buffer
     , windowWidth = windowWidth
     , windowHeight = windowHeight
     , startLine = 0

fcore/app-with.sml

@@ -4,10 +4,17 @@ struct
 
   fun bufferAndSize (app: app_type, newBuffer, newWidth, newHeight) =
     let
-      val {buffer = _, windowWidth = _, windowHeight = _, startLine, cursorIdx} =
-        app
+      val
+        { mode
+        , buffer = _
+        , windowWidth = _
+        , windowHeight = _
+        , startLine
+        , cursorIdx
+        } = app
     in
-      { buffer = newBuffer
+      { mode = mode
+      , buffer = newBuffer
       , windowWidth = newWidth
       , windowHeight = newHeight
       , startLine = startLine
@@ -17,10 +24,12 @@ struct
 
   fun bufferAndCursorIdx (app: app_type, newBuffer, newCursorIdx) =
     let
-      val {buffer = _, cursorIdx = _, windowWidth, windowHeight, startLine} =
+      val
+        {mode, buffer = _, cursorIdx = _, windowWidth, windowHeight, startLine} =
         app
     in
-      { buffer = newBuffer
+      { mode = mode
+      , buffer = newBuffer
       , cursorIdx = newCursorIdx
       , windowWidth = windowWidth
       , windowHeight = windowHeight