matcher: allow hash pattern to omit values.

The @(hash ...) operator now allows key-only patterns
like (42) or (@x), where x could be bound or unbound.
This has separate semantics from when a value is present.

* share/txr/stdlib/match.tl (compile-hash-match): Implement.

* tests/011/patmatch.tl: Test.

* txr.1: Document.

1 files changed, 7 insertions, 0 deletions

diff --git a/tests/011/patmatch.tl b/tests/011/patmatch.tl
index 85adb352..071243fb 100644
--- a/tests/011/patmatch.tl
+++ b/tests/011/patmatch.tl
@@ -187,6 +187,13 @@
       (42))
 
 (mtest
+  (when-match @(hash (a)) #H(() (a b)) t) t
+  (when-match @(hash (c)) #H(() (a b)) t) nil
+  (let ((x 'a)) (when-match @(hash (@x)) #H(() (a b)) t)) t
+  (let ((x 'd)) (when-match @(hash (@x)) #H(() (a b)) t)) nil
+  (when-match @(hash (@x)) #H(() (a b)) x) (a))
+
+(mtest
   (if-match #R(10 20) 10..20 :yes :no) :yes
   (if-match #R(10 20) #R(10 20) :yes :no) :yes
   (if-match #R(10 20) #R(1 2) :yes :no) :no