* module/ice-9/exceptions.scm (guard): Add guard definition that
re-propagates from original continuation, runs consequents in tail
position in guard continuation, and doesn't rewind the stack.
* module/srfi/srfi-34.scm:
* module/rnrs/exceptions.scm (guard): Re-export from (ice-9
exceptions).
* doc/ref/api-modules.texi (Creating Guile Modules): Document
#:re-export-and-replace.
* module/ice-9/boot-9.scm (module-replacements): New module field.
(make-module, make-autoload-interface): Initialize replacements to an
empty hash table.
(resolve-interface): Propagate replacement info when making custom
interfaces.
(define-module): Parse a #:re-export-and-replace keyword arg.
(define-module*): Handle #:re-export-and-replace.
(module-export!, module-re-export!): Add a keyword arg to indicate
whether to replace or not.
(module-replace!): Call module-export! with #:replace? #t.
(duplicate-handlers): Update replace duplicate handler to look for
replacement info on the interfaces.
* module/srfi/srfi-18.scm (srfi):
* module/srfi/srfi-34.scm (srfi): Update to #:re-export-and-replace
raise-continuable as raise.
* libguile/exceptions.c:
* libguile/exceptions.h: New files.
* libguile.h: Add exceptions.h.
* libguile/Makefile.am (libguile_@GUILE_EFFECTIVE_VERSION@_la_SOURCES):
(DOT_X_FILES, DOT_DOC_FILES, modinclude_HEADERS): Add exceptions.c and
exceptions.h.
* libguile/init.c (scm_i_init_guile): Initialize exceptions.
* libguile/threads.c (scm_spawn_thread): Use new names for
scm_i_make_catch_handler and scm_c_make_thunk.
* libguile/throw.c: Rewrite to be implemented in terms of
with-exception-handler / raise-exception.
* libguile/throw.h: Use data types from exceptions.h. Move
scm_report_stack_overflow and scm_report_out_of_memory to
exceptions.[ch].
* module/ice-9/boot-9.scm (&error, &programming-error)
(&non-continuable, make-exception-from-throw, raise-exception)
(with-exception-handler): New top-level definitions.
(throw, catch, with-throw-handler): Rewrite in terms of
with-exception-handler and raise-exception.
: New top-level definitions.
* module/ice-9/exceptions.scm: Adapt to re-export &error,
&programming-error, &non-continuable, raise-exception, and
with-exception-handler from boot-9.
(make-quit-exception, guile-quit-exception-converter): New exception
converters.
(make-exception-from-throw): Override core binding.
* test-suite/tests/eval.test ("inner trim with prompt tag"): Adapt to
"with-exception-handler" being the procedure on the stack.
("outer trim with prompt tag"): Likewise.
* test-suite/tests/exceptions.test (throw-test): Use pass-if-equal.
* module/srfi/srfi-34.scm: Reimplement in terms of core exceptions, and
make "guard" actually re-raise continuations with the original "raise"
continuation.
