If one of the blocks which are subordinate to a @(trailer)

happen to request a successful termination by invoking @(accept)
the position must not advance into the trailer material.

* match.c (v_trailer): Added an unwind protect which
detects that an accept is taking place and adjusts the return value to
restrict the input position at the point given to trailer.
(accept_fail): Use uw_block_return_proto instead of uw_block_return
and pass the symbol as the protocol identifier.

* unwind.c (uw_current_exit_point): New function.
(uw_block_return): Function renamed to uw_block_return_proto;
takes new parameter which is stored in the block structure.

* unwind.h (struct uw_block): New member, protocol.
(uw_block_return): Becomes an inline wrapper for uw_block_return_proto.
(uw_block_return_proto, uw_current_exit_point): Declared.

* txr.1: Interaction between @(trailer) and @(accept) documented.

1 files changed, 7 insertions, 1 deletions

diff --git a/unwind.c b/unwind.c
index 34ef821a..a51ef98f 100644
--- a/unwind.c
+++ b/unwind.c
@@ -192,7 +192,12 @@ uw_frame_t *uw_current_frame(void)
   return uw_stack;
 }
 
-val uw_block_return(val tag, val result)
+uw_frame_t *uw_current_exit_point(void)
+{
+  return uw_exit_point;
+}
+
+val uw_block_return_proto(val tag, val result, val protocol)
 {
   uw_frame_t *ex;
 
@@ -205,6 +210,7 @@ val uw_block_return(val tag, val result)
     return nil;
 
   ex->bl.result = result;
+  ex->bl.protocol = protocol;
   uw_exit_point = ex;
   uw_unwind_to_exit_point();
   abort();