From: "Victor \"Zverok\" Shepelev" <vshepelev@...>
Date: 2007-02-18T20:28:04+09:00
Subject: Re: Pattern matching

>From: Robert Klemme [mailto:shortcutter@googlemail.com]
>On 17.02.2007 20:47, Jon Harrop wrote:
>> I recently got engaged in a thread on comp.lang.functional about ML and
>> Lisp. I posted some simple but efficient OCaml code that is difficult to
>> translate into Lisp:
>>
>> let rec ( +: ) f g = match f, g with
>>   | `Q n, `Q m -> `Q (n +/ m)
>>   | `Q (Int 0), e | e, `Q (Int 0) -> e
>>   | f, `Add(g, h) -> f +: g +: h
>>   | f, g -> `Add(f, g)
>>
>> let rec ( *: ) f g = match f, g with
>>   | `Q n, `Q m -> `Q (n */ m)
>>   | `Q (Int 0), e | e, `Q (Int 0) -> `Q (Int 0)
>>   | `Q (Int 1), e | e, `Q (Int 1) -> e
>>   | f, `Mul(g, h) -> f *: g *: h
>>   | f, g -> `Mul(f, g)
>>
>> let rec simplify = function
>>   | `Q _ | `Var _ as e -> e
>>   | `Add(f, g) -> simplify f +: simplify g
>>   | `Mul(f, g) -> simplify f *: simplify g;;
>>
>> This code does some simple rearrangements of symbolic expressions to
>> simplify them, e.g. 2+1*x+0 -> 2+x. It works with arbitrary-precision
>> rational arithmetic.
>>
>> Does Ruby have pattern matching? If so, what does the above look like in
>> Ruby? If not, how else can you express this elegantly in Ruby?

I've showed kinda pattern matching for Ruby here:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/224528

I'm now working on more full-fledged library (place for it, but no files
still at http://rubyforge.org/projects/pattern-match).

V.