transplant.rb

"""
  I want to store some call tree, like

  > push 1
  > seq do
  >   dup
  >   push 1
  >   drop
  > end
  > swap

  ... and then unleash it on some object.

  Notice, that call results are ignored,
  since in the end I'm only interested in side-effects.
"""

"""
  This object stores any call tree invoked on it.
"""
class Catcher
  def initialize
    @context = [[]]
  end

  def method_missing name, *args
    if block_given? then
      @context.push []
      yield
      chain = @context.pop
      @context.last.push name: name, args: args, do: chain
    else
      @context.last.push name: name, args: args
    end
  end
end

"""
  This method will invoke some call tree on the Catcher
  and return what got stored.
"""
def callTree &block
  catcher = Catcher.new
  catcher.instance_eval &block
  catcher.instance_eval do
    @context.last
  end
end

"""
  This method will replay call tree on the object it is invoked on.
"""
def callTheTree tree
  this = self
  tree.each do |node|
    this.instance_eval do
      if node[:do] then
        this.send node[:name], node[:args] do
          callTheTree node[:do]
        end
      else
        this.send node[:name], node[:args]
      end
    end
  end
end

"""
  This is a test object that just yells any message sent to it into the console.
"""
class Yeller
  def method_missing name, args, &block
    # TODO: replace HAX with proper thingies
    # NOTICE: begin super.[name](args, &block); rescue e; ...; end
    #         doesn't work, it just hangs in a loop
    return super.send name, args, &block if name == :callTheTree

    @indent ||= 0
    put "#{name}(#{args.join ", "})"

    if block_given? then
      put "{"
      @indent += 1
      yield
      @indent -= 1
      put "}"
    end
  end

  def put thing
    puts ("  " * @indent + thing.to_s)
  end
end

# dig the tree out
tree = callTree do
  seq do
    dup
    push 1
    par do
      seq do
        dup
        drop
      end
      drop
    end
  end
end

# plant the tree to the yelling land
Yeller.new.instance_eval do
  callTheTree tree
end