New retry and skip exceptions under restart hierarchy.

* unwind.c (uw_late_init): Register retry and skip symbols
as exception subtypes of restart.

* txr.1: Document retry and skip restarts.

2 files changed, 20 insertions, 1 deletions

diff --git a/txr.1 b/txr.1
index f8a4d0f1..7575b05c 100644
--- a/txr.1
+++ b/txr.1
@@ -40960,7 +40960,11 @@ subtype of every exception type:
 .verb
   t ----+--- warning
         |
-        +--- restart --- continue
+        +--- restart ---+--- continue
+        |               |
+        |               +--- retry
+        |               |
+        |               +--- skip
         |
         +--- error ---+--- type-error
                       |
@@ -41004,6 +41008,19 @@ type. The
 type is intended to be the root of a hierarchy of exception
 types used for denoting restart points: designers are encouraged
 to derive restarts from this type.
+A catch for the
+.code continue
+exception should be established around constructs which can throw an
+error from which it is possible to recover. That exception provides
+the entry point into the recovery which resumes execution.
+A catch for
+.code retry
+should be provided in situations when it is possible and makes sense for a failed
+operation to be tried again.
+A catch for
+.code skip
+should be provided in situations when it is possible and sensible to continue
+with subsequent operations even though an operation has failed.
 
 .NP* Dialect Notes
 
diff --git a/unwind.c b/unwind.c
index 0ac44798..478ac5a4 100644
--- a/unwind.c
+++ b/unwind.c
@@ -1314,6 +1314,8 @@ void uw_late_init(void)
   reg_fun(intern(lit("find-frames-by-mask"), user_package), func_n1(uw_find_frames_by_mask));
 #endif
   uw_register_subtype(continue_s, restart_s);
+  uw_register_subtype(intern(lit("retry"), user_package), restart_s);
+  uw_register_subtype(skip_s, restart_s);
   uw_register_subtype(warning_s, t);
   uw_register_subtype(defr_warning_s, warning_s);
 }