Implement b

spec/atom/vim-mode-spec.coffee

@@ -192,10 +192,41 @@ describe "VimMode", ->
           editor.trigger keydownEvent('w')
           expect(editor.getCursorPosition()).toEqual([3,0])
 
-          editor.setCursorPosition [3,0]
           editor.trigger keydownEvent('w')
           expect(editor.getCursorPosition()).toEqual([3,2])
 
+      describe "the b keybinding", ->
+        it "moves the cursor to the beginning of the previous word", ->
+          editor.buffer.setText(" ab cde1+- \n xyz\n\nzip }\n last")
+          editor.setCursorPosition [4,1]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [3,4]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [3,0]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [2,0]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [1,1]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [0,8]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [0,4]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [0,1]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [0,0]
+
+          editor.trigger keydownEvent('b')
+          expect(editor.getCursorPosition()).toEqual [0,0]
+
     describe "numeric prefix bindings", ->
       it "repeats the following operation N times", ->
         editor.buffer.setText("12345")

src/atom/cursor.coffee

@@ -88,6 +88,28 @@ class Cursor extends View
 
     @setPosition({row, column})
 
+  moveLeftWhile: (regex) ->
+    row = @getRow()
+    column = @getColumn()
+    offset = 0
+
+    matchBackwards = =>
+      line = @editor.buffer.getLine(row)
+      reversedLine = line[0...column].split('').reverse().join('')
+      regex.exec reversedLine
+
+    if not match = matchBackwards()
+      if row > 0
+        row--
+        column = @editor.buffer.getLineLength(row)
+        match = matchBackwards()
+      else
+        column = 0
+
+    offset = match and -match[0].length or 0
+
+    @setPosition [row, column + offset]
+
   updateAppearance: ->
     position = @editor.pixelPositionFromPoint(@point)
     @css(position)

src/atom/vim-mode.coffee

@@ -36,6 +36,7 @@ class VimMode
       'k': 'move-up'
       'l': 'move-right'
       'w': 'move-to-next-word'
+      'b': 'move-to-previous-word'
 
     @handleCommands
       'insert': => @activateInsertMode()
@@ -46,6 +47,7 @@ class VimMode
       'move-down': => new motions.MoveDown @editor
       'move-right': => new motions.MoveRight @editor
       'move-to-next-word': => new motions.MoveToNextWord(@editor)
+      'move-to-previous-word': => new motions.MoveToPreviousWord(@editor)
       'numeric-prefix': (e) => @numericPrefix(e)
 
   bindCommandModeKeys: (bindings) ->

src/atom/vim-mode/motions.coffee

@@ -29,6 +29,10 @@ class MoveDown extends Motion
     {column, row} = @editor.getCursorPosition()
     @editor.moveCursorDown() if row < (@editor.buffer.numLines() - 1)
 
+class MoveToPreviousWord extends Motion
+  execute: ->
+    @editor.cursor.moveLeftWhile /^\s*(\w+|[^A-Za-z0-9_ ]+)/g
+
 class MoveToNextWord extends Motion
   execute: ->
     @editor.setCursorPosition(@nextWordPosition())
@@ -54,4 +58,4 @@ class MoveToNextWord extends Motion
       column = nextLineMatch?.index or 0
     { row, column }
 
-module.exports = { MoveLeft, MoveRight, MoveUp, MoveDown, MoveToNextWord }
+module.exports = { MoveLeft, MoveRight, MoveUp, MoveDown, MoveToNextWord, MoveToPreviousWord }