Comments on: Pattern matching in scheme http://curiousprogrammer.wordpress.com/2006/12/08/pattern-matching-in-scheme/ Leveraging Perl and Emacs Sat, 15 Jun 2013 02:12:16 +0000 hourly 1 http://wordpress.com/ By: Greg Travis http://curiousprogrammer.wordpress.com/2006/12/08/pattern-matching-in-scheme/#comment-221 Sat, 06 Jan 2007 19:44:23 +0000 http://curiousprogrammer.wordpress.com/2006/12/08/pattern-matching-in-scheme/#comment-221 I have been using my own customized version of scheme (it’s a preprocessor). One of my favorite things is a pattern matching syntax that I modeled superficially on Haskell. I tried to make it as concise as possible. It serves both as a destructive
pattern-matching system, a constructor-based algebraic type system, and an overloading system.

It’s only superficially like Haskell — it’s of course latently typed, like regular Scheme. However, I have found it to be incredibly useful. I also used to have the problem that I wrote Scheme with a ‘C++ accent’, and this pattern-matching stuff totally cured me of it.

Below is an example of some code implementing linear transformations for various types.


(fun (scale-to (a . rest) ns)
(cons (scale-to a ns) (scale-to rest ns)))
(fun (scale-to () ns) '())
(fun (scale-to a ns)
(scale a (* ns (/ 1.0 (duration a)))))

(fun (union (Extent a b) (Extent 'everything)) (Extent 'everything))
(fun (union (Extent a b) . rest) (union (Extent a b) (apply union rest)))
(fun (union (Extent 'empty) . rest) (apply union rest))
(fun (union) (Extent 'empty))

(fun (union (Extent a b) (Extent 'empty)) (Extent a b))
(fun (union (Extent 'empty) (Extent c d)) (Extent c d))
(fun (union (Extent 'empty) (Extent 'empty)) (Extent 'empty))

(fun (union (Extent 'empty) . rest) (apply union rest))
(fun (union (Extent 'everything) . rest) (Extent 'everything))

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