‘throw’ introduces a continuation barrier as of Guile 3.0.9:
--8<---------------cut here---------------start------------->8---
$ cat ~/src/guile-debugging/suspendable-continuation.scm
(use-modules (ice-9 control))
(let ((tag (make-prompt-tag)))
(call-with-prompt tag
(lambda ()
(catch #t
(lambda ()
(pk 'suspendable-from-catch? tag (suspendable-continuation? tag))
(throw 'whatever))
(const #t)
(lambda args
(pk 'suspendable-from-exn-handler? tag (suspendable-continuation?
tag)))))
(const #t)))
$ guile ~/src/guile-debugging/suspendable-continuation.scm
;;; (suspendable-from-catch? ("prompt") #t)
;;; (suspendable-from-exn-handler? ("prompt") #f)
--8<---------------cut here---------------end--------------->8---
Apparently this is because that goes through ‘scm_throw’ via
‘intrinsics.c’.
A practical consequence is that a REPL running in Fibers on non-blocking
ports enters an endless “Attempt to suspend fiber within continuation
barrier” loop when it starts a recursive REPL due to an uncaught
exception.
Ludo’.
