Implementation of bash command line history stack in 20 lines of coffeescript. Some tricky corner cases are covered.

gistfile1.coffee

class CommandHistory
  constructor: ->
    @stack = []
    @curPos = -1
    @pushShouldReplaceLast = false

    put = (index, cmd) =>
      if @pushShouldReplaceLast then @stack[index..index] = cmd
      else @stack.push cmd
      @curPos = index
      @pushShouldReplaceLast = false

    move = (detectEnd, changePos, cur) =>
      put @curPos, cur
      if not detectEnd @curPos then changePos()
      @pushShouldReplaceLast = @stack.length > 1 or @curPos < -1
      @stack[@curPos..@curPos]

    @back = _.partial move, ((pos) => pos is -@stack.length), => @curPos--
    @forward = _.partial move, ((pos) => pos is -1), => @curPos++
    @push = _.partial put, -1