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.h b/unwind.h
index c963b1ff..db8a53fa 100644
--- a/unwind.h
+++ b/unwind.h
@@ -43,6 +43,7 @@ struct uw_block {
   uw_frtype_t type;
   val tag;
   val result;
+  val protocol;
   jmp_buf jb;
 };
 
@@ -91,7 +92,11 @@ val uw_get_func(val sym);
 val uw_set_func(val sym, val value);
 val uw_get_match_context(void);
 val uw_set_match_context(val context);
-val uw_block_return(val tag, val result);
+val uw_block_return_proto(val tag, val result, val protocol);
+INLINE val uw_block_return(val tag, val result)
+{
+   return uw_block_return_proto(tag, result, nil);
+}
 void uw_push_catch(uw_frame_t *, val matches);
 noreturn val uw_throw(val sym, val exception);
 noreturn val uw_throwf(val sym, val fmt, ...);
@@ -106,6 +111,7 @@ void uw_push_debug(uw_frame_t *, val func, val args,
                    val line, val chr);
 void uw_pop_frame(uw_frame_t *);
 uw_frame_t *uw_current_frame(void);
+uw_frame_t *uw_current_exit_point(void);
 void uw_init(void);
 
 noreturn val type_mismatch(val, ...);