Return::MultiLevel(3) return across multiple call levels


use Return::MultiLevel qw(with_return);
sub inner {
my ($f) = @_;
$f->(42); # implicitly return from 'with_return' below
print "You don't see this\n";
sub outer {
my ($f) = @_;
print "You don't see this either\n";
my $result = with_return {
my ($return) = @_;
die "Not reached";
print $result, "\n"; # 42


This module provides a way to return immediately from a deeply nested call stack. This is similar to exceptions, but exceptions don't stop automatically at a target frame (and they can be caught by intermediate stack frames using "eval"). In other words, this is more like setjmp(3)/longjmp(3) than "die".

Another way to think about it is that the ``multi-level return'' coderef represents a single-use/upward-only continuation.


The following functions are available (and can be imported on demand).
with_return BLOCK
Executes BLOCK, passing it a code reference (called $return in this description) as a single argument. Returns whatever BLOCK returns.

If $return is called, it causes an immediate return from "with_return". Any arguments passed to $return become "with_return"'s return value (if "with_return" is in scalar context, it will return the last argument passed to $return).

It is an error to invoke $return after its surrounding BLOCK has finished executing. In particular, it is an error to call $return twice.


This module uses "unwind" from "Scope::Upper" to do its work. If "Scope::Upper" is not available, it substitutes its own pure Perl implementation. You can force the pure Perl version to be used regardless by setting the environment variable "RETURN_MULTILEVEL_PP" to 1.

If you get the error message "Attempt to re-enter dead call frame", that means something has called a $return from outside of its "with_return { ... }" block. You can get a stack trace of where that "with_return" was by setting the environment variable "RETURN_MULTILEVEL_DEBUG" to 1.


You can't use this module to return across implicit function calls, such as signal handlers (like $SIG{ALRM}) or destructors ("sub DESTROY { ... }"). These are invoked automatically by perl and not part of the normal call chain.


Lukas Mai, "<l.mai at>"


Copyright 2013-2014 Lukas Mai.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See for more information.