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.IX Title "Return::MultiLevel 3"
.TH Return::MultiLevel 3 2025-07-14 "perl v5.42.0" "User Contributed Perl Documentation"
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.SH NAME
Return::MultiLevel \- Return across multiple call levels
.SH VERSION
.IX Header "VERSION"
version 0.08
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&  use Return::MultiLevel qw(with_return);
\&
\&  sub inner {
\&    my ($f) = @_;
\&    $f\->(42);  # implicitly return from \*(Aqwith_return\*(Aq below
\&    print "You don\*(Aqt see this\en";
\&  }
\&
\&  sub outer {
\&    my ($f) = @_;
\&    inner($f);
\&    print "You don\*(Aqt see this either\en";
\&  }
\&
\&  my $result = with_return {
\&    my ($return) = @_;
\&    outer($return);
\&    die "Not reached";
\&  };
\&  print $result, "\en";  # 42
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This module provides a way to return immediately from a deeply nested call
stack. This is similar to exceptions, but exceptions don\*(Aqt stop automatically
at a target frame (and they can be caught by intermediate stack frames using
\&\f(CW\*(C`eval\*(C'\fR). In other words, this is more like
\&\fBsetjmp\fR\|(3)/\fBlongjmp\fR\|(3) than \f(CW\*(C`die\*(C'\fR.
.PP
Another way to think about it is that the "multi\-level return" coderef
represents a single\-use/upward\-only continuation.
.SS Functions
.IX Subsection "Functions"
The following functions are available (and can be imported on demand).
.IP "with_return BLOCK" 4
.IX Item "with_return BLOCK"
Executes \fIBLOCK\fR, passing it a code reference (called \f(CW$return\fR in this
description) as a single argument. Returns whatever \fIBLOCK\fR returns.
.Sp
If \f(CW$return\fR is called, it causes an immediate return from \f(CW\*(C`with_return\*(C'\fR. Any
arguments passed to \f(CW$return\fR become \f(CW\*(C`with_return\*(C'\fR\*(Aqs return value (if
\&\f(CW\*(C`with_return\*(C'\fR is in scalar context, it will return the last argument passed to
\&\f(CW$return\fR).
.Sp
It is an error to invoke \f(CW$return\fR after its surrounding \fIBLOCK\fR has finished
executing. In particular, it is an error to call \f(CW$return\fR twice.
.SH DEBUGGING
.IX Header "DEBUGGING"
This module uses \f(CW\*(C`unwind\*(C'\fR from
\&\f(CW\*(C`Scope::Upper\*(C'\fR to do its work. If
\&\f(CW\*(C`Scope::Upper\*(C'\fR is not available, it substitutes its own pure
Perl implementation. You can force the pure Perl version to be used regardless
by setting the environment variable \f(CW\*(C`RETURN_MULTILEVEL_PP\*(C'\fR to 1.
.PP
If you get the error message \f(CW\*(C`Attempt to re\-enter dead call frame\*(C'\fR, that means
something has called a \f(CW$return\fR from outside of its \f(CW\*(C`with_return { ... }\*(C'\fR
block. You can get a stack trace of where that \f(CW\*(C`with_return\*(C'\fR was by setting
the environment variable \f(CW\*(C`RETURN_MULTILEVEL_DEBUG\*(C'\fR to 1.
.SH CAVEATS
.IX Header "CAVEATS"
You can\*(Aqt use this module to return across implicit function calls, such as
signal handlers (like \f(CW$SIG{ALRM}\fR) or destructors (\f(CW\*(C`sub DESTROY { ... }\*(C'\fR).
These are invoked automatically by perl and not part of the normal call chain.
.SH AUTHORS
.IX Header "AUTHORS"
.IP \(bu 4
Lukas Mai
.IP \(bu 4
Graham Ollis <plicease@cpan.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is copyright (c) 2013,2014,2021 by Lukas Mai.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.