A puzzle Re: Decorators for multimethods

Roman Suzi rnd at onego.ru
Fri Dec 10 22:26:58 CET 2004


For those who want to exercize Python skills, there is a problem
below for defining multimethod g with as simple syntax as possible:

    @MULTIMETHOD
    def g(x, y):
        @PART(Foo, Foo)
        def m1(a, b): return 'foofoo'

        @PART(Foo, Bar)
        def m2(a, b): return 'foobar'

        @PART(Bar, Foo)
        def m3(a, b): return 'barfoo'


What are definitions of MULTIMETHOD and PART in this case?
(if such are at all possible).

My best result was with

    class G(MMCLASS):
      def define(self):
        @self.PART(Foo, Foo)
        def m1(a, b): return 'foofoo'

        @self.PART(Foo, Bar)
        def m2(a, b): return 'foobar'

        @self.PART(Bar, Foo)
        def m3(a, b): return 'barfoo'

    g = G()

where

    class MMCLASS(Multimethod.Generic):
     def __init__(self):
      Multimethod.Generic.__init__(self)
      def PART(*args):
        def make_multimethod(func):
          mm = Multimethod.Method(tuple(args), func)
          print func
          self.add_method(mm)
          return mm
        return make_multimethod
      self.PART = PART
      self.define()


On Fri, 10 Dec 2004, Roman Suzi wrote:

>
>hi!
>
>I've found one more nice use case for decorators. I feel multimethods
>could be made even nicier by defining multimethods inside special
>class. But I have not figured out how to do it yet.
>
>#!/bin/env python2.4
>if "We have Neel Krishnaswami module Multimethod.py":
>
>    import Multimethod
>
>    class Foo: pass
>
>    class Bar(Foo): pass
>
>    def multimethod(g, *args):
>      def make_multimethod(func):
>        mm = Multimethod.Method(tuple(args), func)
>        g.add_method(mm)
>        return mm
>      return make_multimethod
>
>    g = Multimethod.Generic()
>
>    @multimethod(g, Foo, Foo)
>    def m1(a, b): return 'foofoo'
>
>    @multimethod(g, Foo, Bar)
>    def m2(a, b): return 'foobar'
>
>    @multimethod(g, Bar, Foo)
>    def m3(a, b): return 'barfoo'
>
>    try:
>        print 'Argtypes ', 'Result'
>        print 'Foo, Foo:', g(Foo(), Foo())
>        print 'Foo, Bar:', g(Foo(), Bar())
>        print 'Bar, Foo:', g(Bar(), Foo())
>        print 'Bar, Bar:', g(Bar(), Bar())
>    except Multimethod.AmbiguousMethodError:
>        print 'Failed due to AmbiguousMethodError'
>
>
>Sincerely yours, Roman Suzi
>

Sincerely yours, Roman Suzi
-- 
rnd at onego.ru =\= My AI powered by GNU/Linux RedHat 7.3



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