Bugfix: repeated expansion of catch unstable.

It turns out we have a silly problem: catch is a special
operator, which undergoes a macro-like expansion which alters
its syntax, but uses the same operator symbol.

We turn catch into a macro which expands to a sys:catch
operator.

* eval.c (sys_catch_s): New symbol variable.
(expand_catch): Function now expands sys:catch forms
without altering any syntax.
(do_expand): Check for sys:catch rather than catch.
Call expand_catch differently: it takes the form now
instead of just the arguments, so it can return the
original form if no expansion takes place.
(eval_init): Initialize sys_catch_s variable. Change
registration of op_catch to sys:catch symbol.

* lisplib.c (except_set_entries): Add catch to the
list of autoload symbols for except.tl.

* share/txr/stdlib/except.tl (catch): New macro for
transforming catch to sys:catch.

* txr.1: Reclassify catch operator as a macro.

1 files changed, 1 insertions, 1 deletions

diff --git a/lisplib.c b/lisplib.c
index 76e142e8..2423274a 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -239,7 +239,7 @@ static val hash_instantiate(val set_fun)
 static val except_set_entries(val dlt, val fun)
 {
   val name[] = {
-    lit("handle"), lit("ignwarn"), lit("macro-time-ignwarn"),
+    lit("catch"), lit("handle"), lit("ignwarn"), lit("macro-time-ignwarn"),
     nil
   };
   set_dlt_entries(dlt, name, fun);