Rebinding a Proc

ruby-talk
1

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

2

Sorry to respond to my own message, but sometimes it helps to write these
things out. Here's how I did it (look for changes in the RHDL class below):

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

class RHDL
class << self
   def instance(*args) #clones this class.
     puts "instance:self is: #{self}"
     klass = self.clone
     puts "klass.class is: #{klass.class}"

       @ubm.bind(klass) #bind the unboundmethod to the cloned class
       meth = klass.method(:do_it) #get a method object from the newly
                                   # bound 'do_it' method.

       klass.set_behavior &meth #set cloned class' @__behavior proc
                                   #to the new method object
                                   #('&' converts to proc)

     klass
   end
   def define_behavior(&b)
     @__behavior = b

       self.class.send(:define_method, :do_it, &b) #define a 'do_it' method
       @ubm = self.class.instance_method(:do_it) #create an unbound method

     puts "@behavior.class is: #{@__behavior.class}"
   end

     #add a set_behavior method:
     def set_behavior &b
       @__behavior = b
     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

Now it seems to work:

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

a = AndGate.instance()
a.a=0; a.b=0
a.run #=> 0 #a now is independent of AndGate

....seems to work, but it also seems a bit convoluted :wink:

Phil

3

You might want to replace this:

@__behavior.call

.... with this:

instance_eval(&@__behavior)

gegroet,
Erik V. - http://www.erikveen.dds.nl/