# [plt-scheme] match question

The general answer is the all ... patterns are greedy, but in order,
from left to right.
So we match as many elements to `x' as possible, then one to `y', then
as many to `z' as possible, then another to the second `y'.
In the particular case, we match as many elements to `x' as possible,
while allowing the whole pattern to match. That's the first 3
elements, and the fifth element gets matched to `z'. In your second
example, we have to match at least two elements to `z', so we only
match 2 to `x'.
Does that help explain things?
sam th
On Sat, May 10, 2008 at 6:52 PM, praimon <praimon at gmail.com> wrote:
>* hello,
*>* in 3.99.0.24, using scheme/match:
*>*
*>* (map (lambda (x)
*>* (match x ((list x ... y z ..1 y) (append x z))))
*>* '((1 2 3 4 3)
*>* (1 2 3 4 3 4)
*>* (1 2 3 4 3 3)))
*>*
*>* => ((1 2 4) (1 2 3 3) (1 2 3 3))
*>*
*>* I understand the first two matches, but
*>* shouldn't the last result be (1 2 4 3)?
*>*
*>* This produces my expected answer:
*>*
*>* (match '(1 2 3 4 3 3)
*>* ((list x ... y z ..2 y) (append x z)))
*>*
*>* => (1 2 4 3)
*>*
*>* but in this context, aren't ..1 and ..2 equivalent?
*>*
*>* thanks,
*>* praimon
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--
sam th
samth at ccs.neu.edu