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From: boley@cs.umn.edu (Daniel Boley)
Newsgroups: comp.lang.scheme
Subject: Re: Destructuring / pattern-matching (was: Multiple return values)
Message-ID: <1991Apr16.001511.14500@cs.umn.edu>
Date: 16 Apr 91 00:15:11 GMT
References: <9104130136.AA06792@kuwait> <9104151633.AA16272@garlic.Stanford.EDU>
Organization: University of Minnesota, Minneapolis, CSci dept.
Lines: 27

Is this too simple a way to destructure a list of values?
Here we locally destructure the first 3 elements of the list
	multiple-values-as-a-list
into 3 local variables and as well as getting the cdddr in rest.

; first define this simple fcn.....
(define (give value form)    ; give value to a function
	(apply form value))

; use GIVE to destructure a list of multiple values...
(give multiple-values-as-a-list
      (lambda (variable-1 variable-2 variable-3 . rest)
	      expr-to-evaled-with-destructured-bindings))

; A macro is unnecessary, but if you used a macro, it could look like...
; (this needs a better mnemonic name)
(give-macro (variable-1 variable-2 variable-3 . rest)
	    multiple-values-as-a-list
	    expr-to-be-evaled-with-destructured-bindings)

Of course, a single value handled this way will be a list of one item, so it
won't be as transparent as MULTIPLE-VALUE-BIND, yet it seems so simple.

By just extending the lambda form so that the list of formals can be a
list of lists, one can make this quite general...
- Dan Boley
  boley@cs.umn.edu