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author | Andy Wingo <wingo@pobox.com> | 2016-12-12 20:55:08 +0100 |
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committer | Andy Wingo <wingo@pobox.com> | 2016-12-12 21:13:00 +0100 |
commit | 6dd87f4d8c764360c8d22c03f65603ea8b8c9e78 (patch) | |
tree | 6a502663cd206f0b4a46f61e8eb090ba4bd2e78b /doc/ref/api-control.texi | |
parent | bf4a97898beac167e8b4f565ce4c7540bed24685 (diff) | |
download | guile-6dd87f4d8c764360c8d22c03f65603ea8b8c9e78.tar.gz |
Add suspendable-continuation?
* doc/ref/api-control.texi (Prompt Primitives): Document
suspendable-continuation?.
* libguile/control.c (scm_suspendable_continuation_p): New procedure.
(scm_init_ice_9_control): New extension procedure, defines
suspendable-continuation?.
(scm_init_control): Register scm_init_ice_9_control.
* libguile/eval.c (eval):
* libguile/throw.c (catch):
* libguile/continuations.c (scm_i_make_continuation): Restore resumable
prompt cookie after continuation invocation.
* libguile/vm.c (scm_call_n): Arrange to set resumable_prompt_cookie
during invocation of VM.
* libguile/vm.h (struct scm_vm): Add resumable_prompt_cookie member.
* module/ice-9/control.scm: Export suspendable-continuation?.
* test-suite/tests/control.test ("suspendable-continuation?"): New
test.
Diffstat (limited to 'doc/ref/api-control.texi')
-rw-r--r-- | doc/ref/api-control.texi | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/doc/ref/api-control.texi b/doc/ref/api-control.texi index f0ded98a2..73fbe3607 100644 --- a/doc/ref/api-control.texi +++ b/doc/ref/api-control.texi @@ -628,6 +628,33 @@ This is equivalent to @code{(call/ec (lambda (@var{k}) @var{body} @dots{}))}. @end deffn +Additionally there is another helper primitive exported by @code{(ice-9 +control)}, so load up that module for @code{suspendable-continuation?}: + +@example +(use-modules (ice-9 control)) +@end example + +@deffn {Scheme Procedure} suspendable-continuation? tag +Return @code{#t} if a call to @code{abort-to-prompt} with the prompt tag +@var{tag} would produce a delimited continuation that could be resumed +later. + +Almost all continuations have this property. The exception is where +some code between the @code{call-with-prompt} and the +@code{abort-to-prompt} recursed through C for some reason, the +@code{abort-to-prompt} will succeed but any attempt to resume the +continuation (by calling it) would fail. This is because composing a +saved continuation with the current continuation involves relocating the +stack frames that were saved from the old stack onto a (possibly) new +position on the new stack, and Guile can only do this for stack frames +that it created for Scheme code, not stack frames created by the C +compiler. It's a bit gnarly but if you stick with Scheme, you won't +have any problem. + +If no prompt is found with the given tag, this procedure just returns +@code{#f}. +@end deffn @node Shift and Reset @subsubsection Shift, Reset, and All That |