New catch** macro.

* lisplib.c (except_set_entries): Autoload for catch** symbol.

* share/txr/stdlib/except.tl (catch**): New macro.

* txr.1: Document catch** macro, and the desc slot of
the catch-frame struct.

1 files changed, 29 insertions, 1 deletions

diff --git a/txr.1 b/txr.1
index 9fcfaf13..2a9afa9b 100644
--- a/txr.1
+++ b/txr.1
@@ -38662,6 +38662,8 @@ string and additional arguments.
 .mets \ \  >> {( symbol <> ( arg *) << body-form *)}*)
 .mets (catch* < try-expression
 .mets \ \  >> {( symbol >> ( type-arg << arg *) << body-form *)}*)
+.mets (catch** < try-expression
+.mets \ \  >> {( symbol < desc >> ( type-arg << arg *) << body-form *)}*)
 .syne
 .desc
 The
@@ -38728,6 +38730,19 @@ Then the exception arguments follow. In contrast,
 only the exception arguments are passed to the clauses of
 .codn catch .
 
+The
+.code catch**
+macro is a further variant, which differs from
+.code catch*
+by requiring each catch clause to provide a description
+.metn desc ,
+an expression which evaluates to a character string.
+The
+.meta desc
+expressions are evaluated in left-to-right order prior to the
+evaluation of
+.metn try-expression .
+
 Also see: the
 .code unwind-protect
 operator, and the functions
@@ -39297,7 +39312,7 @@ and not a derived representation.
 .coNP Structures @, frame @ catch-frame and @ handle-frame
 .synb
 .mets (defstruct frame nil)
-.mets (defstruct catch-frame frame types jump)
+.mets (defstruct catch-frame frame types desc jump)
 .mets (defstruct handle-frame frame types fun)
 .syne
 .desc
@@ -39341,6 +39356,19 @@ slot. This holds the list of exception type symbols which are matched
 by the catch or handler.
 
 The
+.code desc
+slot of a
+.code catch-frame
+holds a list of the descriptions produced by the
+.code catch**
+macro. If there are no descriptions, then this member is
+.codn nil ,
+otherwise it is a list whose elements are in correspondence
+with the list in the
+.code types
+slot.
+
+The
 .code jump
 slot of a
 .code catch-frame