txr: support variable in postive match.

In the @{var mod} syntax in the pattern language, allow mod to
be a variable which contains a regex or integer, not just an
integer or regex literal.

* match.c (h_var): Check for modifier being a variable, and
resolve it.

* parser.y (modifiers): Allow a SYMTOK phrase.

* txr.1: Documented.

1 files changed, 5 insertions, 0 deletions

diff --git a/match.c b/match.c
index 3a1024e9..a7a65098 100644
--- a/match.c
+++ b/match.c
@@ -596,6 +596,11 @@ static val h_var(match_line_ctx *c)
               sym, nao);
   }
 
+  if (bindable(modifier)) {
+    val mpair = tx_lookup_var_ubc(modifier, c->bindings, elem);
+    modifier = cdr(mpair);
+  }
+
   if (pair) {
     /* If the variable already has a binding, we replace
        it with its value, and treat it as a string match.