Relaxing :vars in collect/coll a little bit.

* match.c (h_coll, v_collect): Only throw an error about
missing required variables if the collect iteration collected some new
variables.  This allows strict collects with :vars to have
some cases which explicitly match and skip unwanted material,
without binding variables.  Also, print all missing variables in the
diagnostic.

* txr.1: Mention this special exception.

* RELNOTES: Updated.

4 files changed, 36 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 67e71097..ce7a90f3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+2011-11-20  Kaz Kylheku  <kaz@kylheku.com>
+
+	Relaxing :vars in collect/coll a little bit.
+
+	* match.c (h_coll, v_collect): Only throw an error about
+	missing required variables if the collect iteration collected some new
+	variables.  This allows strict collects with :vars to have
+	some cases which explicitly match and skip unwanted material,
+	without binding variables.  Also, print all missing variables in the
+	diagnostic.
+
+	* txr.1: Mention this special exception.
+
+	* RELNOTES: Updated.
+
 2011-11-19  Kaz Kylheku  <kaz@kylheku.com>
 
 	* Makefile (tests/008/soundex.ok): New test case.
diff --git a/RELNOTES b/RELNOTES
index 79e7043c..20142bdb 100644
--- a/RELNOTES
+++ b/RELNOTES
@@ -38,6 +38,11 @@ Version 042
   - Stability fix: several long-time uninitialized variable bugs found,
     and some faulty object initialization orders.
 
+  - :vars in @(collect)/@(coll) does not fire an exception about missing
+    required variables if no variable bindings are produced at all,
+    allowing strict collects to have explicit matches for unwanted material
+    without triggering this nuisance error.
+
   Internal
 
   - New infrastructure for matching location info to source forms.
diff --git a/match.c b/match.c
index 3df2656c..05b542bd 100644
--- a/match.c
+++ b/match.c
@@ -740,8 +740,10 @@ static val h_coll(match_line_ctx c, match_line_ctx *cout)
       }
 
       if (new_pos) {
+        list_collect_decl (missing, ptail);
         val strictly_new_bindings = set_diff(new_bindings,
                                              c.bindings, eq_f, nil);
+        val have_new = strictly_new_bindings;
         LOG_MATCH("coll", new_pos);
 
         for (iter = vars; iter; iter = cdr(iter)) {
@@ -750,14 +752,17 @@ static val h_coll(match_line_ctx c, match_line_ctx *cout)
 
           if (!exists) {
             if (dfl == noval_s)
-              sem_error(elem, lit("coll failed to bind ~a"),
-                        var, nao);
+              list_collect (ptail, var);
             else
               strictly_new_bindings = acons(strictly_new_bindings, 
                                             var, dfl);
           }
         }
 
+        if (have_new && missing)
+          sem_error(elem, lit("collect failed to bind ~a"),
+                    missing, nao);
+
         for (iter = strictly_new_bindings; iter; iter = cdr(iter))
         {
           val binding = car(iter);
@@ -2305,8 +2310,10 @@ static val v_collect(match_files_ctx *c)
       }
 
       if (success) {
+        list_collect_decl (missing, ptail);
         val strictly_new_bindings = set_diff(new_bindings,
                                              c->bindings, eq_f, nil);
+        val have_new = strictly_new_bindings;
 
         debuglf(specline, lit("collect matched ~a:~a"),
                 first(c->files), c->data_lineno, nao);
@@ -2317,14 +2324,17 @@ static val v_collect(match_files_ctx *c)
 
           if (!exists) {
             if (dfl == noval_s) 
-              sem_error(specline, lit("collect failed to bind ~a"),
-                        var, nao);
+              list_collect (ptail, var);
             else
               strictly_new_bindings = acons(strictly_new_bindings, 
                                             var, dfl);
           }
         }
 
+        if (have_new && missing)
+          sem_error(specline, lit("collect failed to bind ~a"),
+                    missing, nao);
+
         for (iter = strictly_new_bindings; iter; iter = cdr(iter))
         {
           val binding = car(iter);
diff --git a/txr.1 b/txr.1
index 17c4307c..0953dfef 100644
--- a/txr.1
+++ b/txr.1
@@ -2062,6 +2062,8 @@ variables do not propagate.
 Furthermore, for any variable which is not specified with a default value, the
 collect body, whenever it matches successfully, must bind that variable. If it
 neglects to bind the variable, an exception of type query_error is thrown.
+(If a collect body matches successfully, but produces no new bindings, then
+this error is suppressed.)
 
 For any variable which does have a default value, if the collect body neglects
 to bind that variable, the behavior is as if the collect did bind that variable