animator.rb

## walking.seq.rb
index 1
repeat do
  rest 0.1
  succ
  rest 0.1
  succ
  rest 0.1
  pred
  rest 0.1
  pred
  cancel
end

## animator.rb
class Animator

  class Builder

    def initialize
      @_list = []
      @_depth = 0
    end

    def render
      @_list
    end

    def _cmd(sym, *params)
      @_list << [@_depth, sym, *params]
    end

    def _depth_succ
      @_depth += 1
    end

    def _depth_pred
      @_depth -= 1
    end

    def _import(data)
      instance_eval(data); self
    end

    def index(n)
      _cmd(:index, n.to_i)
    end

    def succ(n=1)
      _cmd(:succ, n.to_i)
    end

    def pred(n=1)
      _cmd(:pred, n.to_i)
    end

    def rest(n)
      _cmd(:rest, n.to_i)
    end

    def repeat
      @_list << _cmd(:repeat)
      _depth_succ
      yield
      _depth_pred
      @_list << _cmd(:end)
    end

    def cancel
      _cmd(:cancel)
    end

    def self.build(data)
      new._import(data)
    end

  end

  def initialize
    clear
  end

  def clear
    @_list = nil
    @_list_index = 0
    @_depth = 0
    @_depth_flags = [[]]
    @_depth_vars = [{}]
  end

  def depth_succ
    @_depth += 1
    @_depth_flags.push([])
    @_depth_vars.push({})
  end

  def depth_pred
    @_depth -= 1
    @_depth_flags.pop
    @_depth_vars.pop
  end

  def depth_vars
    @_depth_vars[@_depth]
  end

  def depth_flags
    @_depth_flags[@_depth]
  end

  def exec_command(cmd)
    dp, op, *params = *cmd
    case op
    when :index # set the index
      @index = params.first
    when :succ # increment index
      @index += params.first
    when :pred # decrement index
      @index -= params.first
    when :rest # sleep for a period
      @rest = (params.first * Graphics.frame_rate).to_i
    when :repeat
      depth_succ
      depth_flags << :repeat
      depth_vars[:line] = @_list_index
    when :cancel
      depth_pred
    when :end
      if depth_flags.include?(:repeat)
        @_list_index = depth_vars[:line]
      else
        depth_flags.delete(:repeat)
      end
    end
  end

  def current_line
    @_list[@_list_index]
  end

  def update
    if @rest > 0
      @rest -= 1
    else
      if @_list
        while @_list.size > @_list_index
          exec_command(current_line)
          while current_line[0] > @_depth #.depth
            @_list_index += 1
            break if @_list.size < @_list_index
          end
        end
      end
    end
  end

end

require 'pp'
pp Animator::Builder.build(File.read("../../data/sequence/animation/walking.seq.rb")).render