matcher: new @(coll) operator.

* share/txr/stdlib/match.tl (compile-loop-match): Implement
coll semantics. coll fails if it collects nothing, which
uses common logic with all*. We just have to move the
flipping of the loop-iterated-var into the match, and not
do it unconditionally for every iteration.
(compile-match): Hook in the coll operator.

* tests/011/patmatch.tl: Test case copied from doc example.

* txr.1: Documented.

1 files changed, 29 insertions, 1 deletions

diff --git a/txr.1 b/txr.1
index ce6f045f..5fbf346f 100644
--- a/txr.1
+++ b/txr.1
@@ -40109,7 +40109,7 @@ The specified
 .meta pattern
 is applied against every element of the sequence. The match is successful if
 .meta pattern
-finds a matching element.
+matches at least one element.
 
 Variables are extracted from the first matching which is found.
 
@@ -40125,6 +40125,34 @@ Variables are extracted from the first matching which is found.
   -> (2 b)
 .brev
 
+.coNP Pattern operator @ coll
+.synb
+.mets @(coll << pattern )
+.syne
+.desc
+The
+.code coll
+pattern operator requires the corresponding object to be a sequence.
+The specified
+.meta pattern
+is applied against every element of the sequence. The match is successful if
+.meta pattern
+matches at least one element.
+
+Variables are extracted from all matching elements, and collected into
+parallel lists, just like with the
+.code @(all)
+operator.
+
+.TP* Example:
+
+.verb
+  (when-match @(coll (x @a @b))
+             '((y 1 a) (x 2 b) (z 3 c) (x 4 d))
+    (list a b))
+  -> ((2 4) (b d))
+.brev
+
 .coNP Pattern operators @ and and @ or
 .synb
 .mets @(and << pattern *)