From a5f90cf8a467ac8817ab3db5c9f8190b7a547d67 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 22 Jan 2021 00:17:46 -0800
Subject: matcher: existing variables in @(all) now backref.
This commit fixes the inadequacy that all variables occurring
in a pattern under @(all ...) or @(coll ...) are blindly
collated into lists, ignoring the fact that they may be
previously bound variables that must back-reference and not be
colleced into lists (just like in the TXR Pattern language!)
* share/txr/stdlib/match.tl (compile-loop-match): Calculate
the subset of variables in the pattern that have been freshly
bound. Only generate the collection gensyms for those
variables and only collect and nreverse those variables.
* tests/011/patmatch.tl: Some test cases that backreference
into an @(all).
* txr.1: Documented.
---
txr.1 | 29 ++++++++++++++++++++++++++---
1 file changed, 26 insertions(+), 3 deletions(-)
(limited to 'txr.1')
diff --git a/txr.1 b/txr.1
index e2f88973..45800d08 100644
--- a/txr.1
+++ b/txr.1
@@ -40066,10 +40066,15 @@ is applied against every element of the sequence. The match is successful if
.meta pattern
matches every element.
-Furthermore, in the case of a successful match, these operators take
-each of the variables specified in the
+Furthermore, in the case of a successful match, each variable that
+is freshly bound by
.meta pattern
-and bind it to a list of the elements which that variable matched.
+is converted into a list of all of the objects which that variable
+encounters from all elements of the sequence. Those variables which already
+have a binding from another
+.meta pattern
+are not converted to lists. Their existing values are merely required to match
+each corresponding object they encounter.
The difference between
.code all
@@ -40095,6 +40100,15 @@ operator behaves like a failed match when the sequence is empty.
'((x 1 a) (x 2 b) (x 3 c))
(list a b))
--> ((1 2 3) (a b c))
+
+ ;; Match a two element list whose second element
+ ;; consists of nothing but zero or more repetitions
+ ;; of the first element. x is not turned into a list
+ ;; because it has a binding due to @x.
+ (when-match @(@x @(all x)) '(1 (1 1 1 1)) x) -> 1
+
+ ;; no match because of the 2
+ (when-match @(@x @(all x)) '(1 (1 1 1 2)) x) -> nil
.brev
.coNP Pattern operator @ some
@@ -40139,6 +40153,15 @@ is applied against every element of the sequence. The match is successful if
.meta pattern
matches at least one element.
+Each variable that is freshly bound by the
+.meta pattern
+is converted into a list of all of the objects which that variable
+encounters from the matching elements of the sequence. Those variables which
+already have a binding from another
+.meta pattern
+are not converted to lists. Their existing values are merely required to match
+each corresponding object they encounter.
+
Variables are extracted from all matching elements, and collected into
parallel lists, just like with the
.code @(all)
--
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