reimplemented vi's 'B' command (although it needs a little refactoring)

fcore/cursor-dfa/vi-WORD-dfa.sml

@@ -3,7 +3,8 @@ struct
   val startState: Word8.word = 0w0
   val startNonBlankState: Word8.word = 0w1
   val startSpaceState: Word8.word = 0w2
-  val nonBlankAfterSpaceState: Word8.word = 0w4
+  val nonBlankAfterSpaceState: Word8.word = 0w3
+  val spaceAfterNonBlankState = 0w4
 
   fun makeStart i =
     let val chr = Char.chr i
@@ -12,7 +13,7 @@ struct
 
   fun makeStartNonBlankState i =
     let val chr = Char.chr i
-    in if Char.isSpace chr then startSpaceState else startNonBlankState
+    in if Char.isSpace chr then spaceAfterNonBlankState else startNonBlankState
     end
 
   fun makeStartSpace i =
@@ -20,11 +21,27 @@ struct
     in if Char.isSpace chr then startSpaceState else nonBlankAfterSpaceState
     end
 
+  fun makeNonBlankAfterSpace i =
+    let
+      val chr = Char.chr i
+    in
+      if Char.isSpace chr then spaceAfterNonBlankState
+      else nonBlankAfterSpaceState
+    end
+
   val startTable = Vector.tabulate (255, makeStart)
   val startNonBlankTable = Vector.tabulate (255, makeStartNonBlankState)
   val startSpaceTable = Vector.tabulate (255, makeStartSpace)
+  val nonBlankAfterSpaceTable = Vector.tabulate (255, makeNonBlankAfterSpace)
+  val spaceAfterNonBlankTable = nonBlankAfterSpaceTable
 
-  val tables = #[startTable, startNonBlankTable, startSpaceTable]
+  val tables =
+   #[ startTable
+    , startNonBlankTable
+    , startSpaceTable
+    , nonBlankAfterSpaceTable
+    , spaceAfterNonBlankTable
+    ]
 
   fun next (currentState, currentChar) =
     let
@@ -91,6 +108,39 @@ struct
              end
        end)
 
+  structure StartOfCurrentWORD =
+    MakePrevDfaLoop
+      (struct
+         val startState = startState
+
+         fun fStart (idx, absIdx, str, tl, currentState, counter) =
+           if idx < 0 then
+             case tl of
+               str :: tl =>
+                 fStart
+                   (String.size str - 1, absIdx, str, tl, currentState, counter)
+             | [] => 0
+           else
+             let
+               val chr = String.sub (str, idx)
+               val newState = next (currentState, chr)
+             in
+               if newState = spaceAfterNonBlankState then
+                 if counter - 1 = 0 then
+                   absIdx + 1
+                 else
+                   fStart
+                     (idx - 1, absIdx - 1, str, tl, startState, counter - 1)
+               else
+                 fStart (idx - 1, absIdx - 1, str, tl, newState, counter)
+             end
+       end)
+
   val startOfNextWORD = StartOfNextWORD.next
   val endOfPrevWORD = EndOfPrevWORD.prev
+
+  fun startOfCurrentWORD (lineGap: LineGap.t, cursorIdx) =
+    let val lineGap = LineGap.goToIdx (cursorIdx - 1, lineGap)
+    in StartOfCurrentWORD.prev (lineGap, cursorIdx - 1)
+    end
 end

fcore/cursor.sml

@@ -1038,8 +1038,7 @@ struct
     toPrevWord (lineGap, cursorIdx, helpPrevWord)
 
   (* equivalent of vi's 'B' command *)
-  fun prevWORD (lineGap, cursorIdx) =
-    toPrevWord (lineGap, cursorIdx, helpPrevWORD)
+  val prevWORD = ViWORDDfa.startOfCurrentWORD
 
   fun toEndOfPrevWord (lineGap: LineGap.t, cursorIdx, fPrev) =
     let