From: ptkwt@... (Phil Tomson)
Date: 2006-02-11T05:43:23+09:00
Subject: rebinding a Proc


Weird stuff ahead.  I'm making (actually, remaking) a DSL.  I'm re-visioning 
RHDL to take more advantage of metaprogramming tricks.

So I'd like the user to be able to declare a logic gate like so:

  class AndGate < RHDL
    inputs  :a, :b
    inouts  :bus
    outputs :a_and_b

    define_behavior {
      puts "Inside of define_behavior: a is: #{a}, b is: #{b}"
      a_and_b = a & b
    }
 end

And then the user should be able to instantiate an AndGate like so:

  andg = AndGate.instance() #optional args


The 'inputs', 'inouts' and 'outputs' methods create accessors for the signals 
at the class level so that they are then accessable in the block passed to 
define_behavior.

Here's some of the background from the RHDL class:

class RHDL
  class << self
    def instance(*args)  #clones this class.
      puts "instance:self is: #{self}"
      klass = self.clone
      puts "klass.class is: #{klass.class}"
      klass
    end
    def define_behavior(&b)
      @__behavior = b 
      puts "@behavior.class is: #{@__behavior.class}"
    end
    def behavior
      @__behavior
    end
    def run
      puts "in #{self}::run"
      puts "a is: #{a}, b is: #{b} "
      @__behavior.call
    end
    def inports
      @__inports ||=[]
    end
    def inoutports
      @__inoutports ||=[]
    end
    def outports
      @__outports ||=[]
    end
    def create_accessor str
      instance_eval "def #{str}=(val); puts \"self is: #{self}\"; @#{str} = 
val; end"
      instance_eval "def #{str}; @#{str} ||=0; end"
    end
    def inputs *in_syms
      in_syms.each {|input|
        inports << Port.new(input.to_s)
        create_accessor input
      }
    end
    #... outputs, inouts, etc.
end


Of course, the problem is in the block passed to the define_behavior method.  
It's defined within the context of the AndGate class definition above, so if 
we clone the AndGate class itself we find that the behavior is still determined 
by the context of the original AndGate class.

So If I do:

  AndGate.a=1; AndGate.b=1
  AndGate.run #=> 1

  a = AndGate.instance()
  a.a=0; a.b=0
  a.run #=> 1  (but should be 0; this is because the block is still evaluated 
                in the context of AndGate class, not the clone of AndGate)


So when the AndGate class is cloned, is there a way to unbind the proc in the 
class' @__behavior class inst var and rebind it in the context of the new 
cloned class? (kind of what can be done with methods and UnboundMethod)

[I realize there are probably other ways to do this where this wouldn't be an 
issue (use a method instead of a proc, for example) but I'm trying to maintain 
compatibility with the backend simulation guts of the current RHDL system.]

Phil