From: Trans <transfire@...>
Date: 2005-09-06T06:56:27+09:00
Subject: Re: Change Binding of a Proc


Florian Gro� wrote:
> Trans wrote:
>
> > I'm able to turn the proc into an instance method, then capture the
> > UnboundMethod, then undefine it, then bind it to the instance in order
> > to call it, but that sure seems like a hek of a round about way to have
> > to do things.
>
> I wonder why you have to call a proc on an instance when it isn't used
> as an instance method. Care to explain?

I'm writing a little parser and one defines a "state-machine" for the
parser to use. In it one defines tokens. The tokens can be paired
having a start and end regexp, but they can be in procs so that they
can react to parsing state. For example:

  class MyMachine < StateParser::StateMachine

    token :xnx, /x(.)x/, proc{ |match,state| /y#{match[1]}y/ }

  end

The above would match on something like "x1x ... y1y". But also the
machine can have event hooks, and with those can also do the above like
this:

  class MyMachine < StateParser::StateMachine

    def initialize
      @stack = []
    end

    token :xnx, /x(.)x/, proc{ |match,state| /y#{@stack.last}y/ }

    def xnx( match, state )
      puts "I just matched #{match[0]}"
      @stack << match[1]
    end

    def end_xnx( match, state )
      puts "I just end matched #{match[0]}"
      @stack.pop
    end

  end

> > Any better solutions?
>
> evil-ruby has Proc#self=. It's not one of the safer methods.

Beleive me, my current solution is evil enough as it is ;-)

T.