From: Simon Strandgaard <0bz63fz3m1qt3001@...>
Date: 2002-10-21T16:53:10+09:00
Subject: Re: Duck patterns in Ruby

On Mon, 21 Oct 2002 02:41:53 +0200
"MikkelFJ" <mikkelfj-anti-spam@bigfoot.com> wrote:

[snip]
> So I thought it would be nice to be able to branch the code based on > whether an argument had the "each" method. This lead to the idea of
> a kind of pattern matching based on available methods instead of the
> more strict matching on a class.
> 
> def product (x, y)
>   p = 0
>   match_methods(x, y)
>     when(:each, nil) x.each {|a| p = p + a.multiply(y) }
>     when(nil, :each) y.each {|b| p = p + x.multiply(b) }
>     when(nil, nil) p = x.multiply(y)
>   end
>   return p
> end
> 
> (Might also be nice to branch based on whether a method yields or takes a
> code block as argument).
> 
> It is somewhat similar to type matching in languages like OCaml, except here
> you match the duck type, not the class type.


Yes, this is pattern-matching ala Standard ML, this is realy nice ;-)
also know as multimethods, double dispatch, visitor.


[snip]

What are your question ?  
do you want multimethods ?


regards
Simon Strandgaard