NAME

       Return::MultiLevel - Return across multiple call levels

VERSION

       version 0.08

SYNOPSIS

         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 ($f) = @_;
           inner($f);
           print "You don't see this either\n";
         }

         my $result = with_return {
           my ($return) = @_;
           outer($return);
           die "Not reached";
         };
         print $result, "\n";  # 42

DESCRIPTION

       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.

   Functions
       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.

DEBUGGING

       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.

CAVEATS

       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.

AUTHORS

       •   Lukas Mai

       •   Graham Ollis <plicease@cpan.org>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2013,2014,2021 by Lukas Mai.

       This is free software; you can redistribute it and/or modify it under the same terms as
       the Perl 5 programming language system itself.