add visualScrollColumn' field to app type, which will record the scroll position for us

fcore/app-type.sml

@@ -17,6 +17,8 @@ struct
     , startLine: int
     (* absolute index of movable cursor *)
     , cursorIdx: int
+    (* column to start drawing text at for horizontal scrolling. *)
+    , visualScrollColumn: int
     (* msgs to send after an update.
      * The list of messages is reset on each invocation of AppUpdate.update. *)
     , msgs: MailboxType.t list
@@ -32,6 +34,7 @@ struct
     , windowHeight = windowHeight
     , startLine = 0
     , cursorIdx = 0
+    , visualScrollColumn = 0
     , msgs = []
     }
 end

fcore/normal-mode/normal-mode-with.sml

@@ -23,6 +23,7 @@ struct
         , searchString
         , startLine
         , cursorIdx
+        , visualScrollColumn
         } = app
     in
       { mode = mode
@@ -35,6 +36,7 @@ struct
       , searchString = searchString
       , startLine = startLine
       , cursorIdx = cursorIdx
+      , visualScrollColumn = visualScrollColumn
       }
     end
 
@@ -60,6 +62,7 @@ struct
         , searchString
         , windowWidth
         , windowHeight
+        , visualScrollColumn
         } = app
     in
       { mode = newMode
@@ -72,6 +75,7 @@ struct
       , searchString = searchString
       , windowWidth = windowWidth
       , windowHeight = windowHeight
+      , visualScrollColumn = visualScrollColumn
       }
     end
 
@@ -88,6 +92,7 @@ struct
         , windowWidth
         , windowHeight
         , startLine
+        , visualScrollColumn
         } = app
     in
       { mode = newMode
@@ -100,6 +105,7 @@ struct
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , startLine = startLine
+      , visualScrollColumn = visualScrollColumn
       }
     end
 
@@ -116,6 +122,7 @@ struct
         , windowWidth
         , windowHeight
         , startLine
+        , visualScrollColumn
         } = app
     in
       { mode = newMode
@@ -128,6 +135,7 @@ struct
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , startLine = startLine
+      , visualScrollColumn = visualScrollColumn
       }
     end
 
@@ -151,6 +159,7 @@ struct
         , windowWidth
         , windowHeight
         , startLine
+        , visualScrollColumn
         } = app
     in
       { searchList = newSearchList
@@ -163,6 +172,7 @@ struct
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , startLine = startLine
+      , visualScrollColumn = visualScrollColumn
       }
     end
 end

fcore/normal-mode/normal-search-mode-with.sml

@@ -23,6 +23,7 @@ struct
         , windowWidth
         , windowHeight
         , cursorIdx
+        , visualScrollColumn
         } = app
     in
       { mode = newMode
@@ -35,6 +36,7 @@ struct
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , cursorIdx = cursorIdx
+      , visualScrollColumn = visualScrollColumn
       }
     end
 
@@ -52,6 +54,7 @@ struct
         , windowWidth
         , windowHeight
         , cursorIdx
+        , visualScrollColumn
         } = app
     in
       { mode = newMode
@@ -64,6 +67,7 @@ struct
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , cursorIdx = cursorIdx
+      , visualScrollColumn = visualScrollColumn
       }
     end
 
@@ -80,6 +84,7 @@ struct
         , windowWidth
         , windowHeight
         , cursorIdx
+        , visualScrollColumn
         } = app
     in
       { mode = mode
@@ -92,6 +97,7 @@ struct
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , cursorIdx = cursorIdx
+      , visualScrollColumn = visualScrollColumn
       }
     end
 
@@ -109,6 +115,7 @@ struct
         , startLine
         , bufferModifyTime
         , cursorIdx
+        , visualScrollColumn
         } = app
     in
       { mode = mode
@@ -121,6 +128,7 @@ struct
       , searchString = searchString
       , bufferModifyTime = bufferModifyTime
       , cursorIdx = cursorIdx
+      , visualScrollColumn = visualScrollColumn
       }
     end
 end