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.

3 files changed, 37 insertions, 8 deletions

diff --git a/share/txr/stdlib/match.tl b/share/txr/stdlib/match.tl
index b95fc627..8cb29622 100644
--- a/share/txr/stdlib/match.tl
+++ b/share/txr/stdlib/match.tl
@@ -221,13 +221,15 @@
            (some-p (eq op 'some))
            (coll-p (eq op 'coll))
            (item-var (gensym "item-"))
+           (in-vars var-list.vars)
            (cm (compile-match match item-var var-list))
            (loop-success-p-var (gensym "loop-success-p-"))
            (loop-continue-p-var (gensym "loop-terminate-p"))
            (loop-iterated-var (if no-vac-p (gensym "loop-iterated-p")))
            (matched-p-var (gensym "matched-p-"))
            (iter-var (gensym "iter-"))
-           (collect-vars [mapcar gensym cm.vars])
+           (collect-vars (diff cm.vars in-vars))
+           (collect-gens [mapcar gensym collect-vars])
            (loop ^(for ((,iter-var (iter-begin ,obj-var))
                         (,loop-continue-p-var t)
                         ,*(if no-vac-p ^((,loop-iterated-var nil))))
@@ -250,12 +252,12 @@
                                        ^((set ,loop-iterated-var t)))
                                    ,*(unless some-p
                                        (mapcar (ret ^(push ,@1 ,@2))
-                                               cm.vars
-                                               collect-vars))))))
+                                               collect-vars
+                                               collect-gens))))))
                       ,(unless coll-p ^(,(if some-p 'when 'unless) ,matched-p-var
                          (set ,loop-continue-p-var nil))))))
            (guard (new match-guard
-                       vars (append cm.vars (unless some-p collect-vars))
+                       vars (append cm.vars (unless some-p collect-gens))
                        guard-expr ^(seqp ,obj-var))))
       (new compiled-match
            pattern exp
@@ -267,7 +269,7 @@
                        loop-success-p-var
                        ^(when ,loop-success-p-var
                           ,*(mapcar (ret ^(set ,@1 (nreverse ,@2)))
-                                    cm.vars collect-vars)
+                                    collect-vars collect-gens)
                           t))))))
 
 (defun compile-parallel-match (par-pat obj-var var-list)
diff --git a/tests/011/patmatch.tl b/tests/011/patmatch.tl
index 11a6a933..2b1e26c8 100644
--- a/tests/011/patmatch.tl
+++ b/tests/011/patmatch.tl
@@ -54,6 +54,10 @@
         (list a b))
       ((1 2 3) (a b c)))
 
+(test (when-match (@x @(all @x)) '(1 (1 1 1 1)) x) 1)
+
+(test (when-match (@x @(all @x)) '(1 (1 1 1 2)) x) nil)
+
 (test (when-match @(some (x @a @b)) '((y 1 a) (x 2 b) (z 3 c))
         (list a b))
       (2 b))
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)