New way of handling exceptions without unwinding.

* eval.c (handler_bind_s): New symbol variable.
(op_handler_bind): New static function.
(do_expand): Traverse handler-bind forms.
(eval_init): Initialize handler_bind_s variable and register handler-bind
operator.

* lisplib.c (except_set_entries, except_instantiate): New functions.
(lisplib_init): Register new functions in dl_table.

* parser.c (intr_s): New symbol variable.
(repl_intr): Throw exception of type intr, rather than error.
This way we can interrupt accidental exception handling loops involving
exceptions derived from error.
(parse_init): Initialize intr_s.

* share/txr/stdlib/except.tl: New file, defines handle macro.

* unwind.c (uw_push_handler): New function.
(invoke_handler): New static function.
(uw_throw): Search loop looks for and processes handlers in addition to
catches.

* unwind.h (uw_frtype_t): New enum member, UW_HANDLE.
(struct uw_catch): Move member visible so it
is in the same position as in struct uw_handler.
(struct uw_handler): New struct type.
(union uw_frame): New member ha of type struct uw_handler.
(uw_push_handler): Function declared.

* txr.1: Added introductory paragraphs to Exception Handling section.
Documented handler-bind and handle. Some minor errors corrected.

1 files changed, 16 insertions, 0 deletions

diff --git a/lisplib.c b/lisplib.c
index 53898c08..cb4fdb48 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -228,6 +228,21 @@ static val hash_instantiate(val set_fun)
   return nil;
 }
 
+static val except_set_entries(val dlt, val fun)
+{
+  val name[] = { lit("handle"), nil };
+  set_dlt_entries(dlt, name, fun);
+  return nil;
+}
+
+static val except_instantiate(val set_fun)
+{
+  funcall1(set_fun, nil);
+  load(format(nil, lit("~a/except.tl"), stdlib_path, nao));
+  return nil;
+}
+
+
 val dlt_register(val dlt,
                  val (*instantiate)(val),
                  val (*set_entries)(val, val))
@@ -248,6 +263,7 @@ void lisplib_init(void)
   dlt_register(dl_table, struct_instantiate, struct_set_entries);
   dlt_register(dl_table, with_stream_instantiate, with_stream_set_entries);
   dlt_register(dl_table, hash_instantiate, hash_set_entries);
+  dlt_register(dl_table, except_instantiate, except_set_entries);
 }
 
 val lisplib_try_load(val sym)