#!/usr/bin/env perl -l

use strict;
use warnings;

# Compile time
use if $ENV{PM_1155832_USE}, 'List::Util' => qw{max};

BEGIN {
    print 'Check for List::Util::max() at compile time';
    eval { max(1, 2) };
    print $@ if $@;
}

# Runtime
if (! $ENV{PM_1155832_USE}) {
    require List::Util;
    List::Util->import(qw{max});
}

print 'Max is ', max(1, 2);

##</code><code>##

$ pm_1155832_cond_use_mod.pl
Check for List::Util::max() at compile time
Undefined subroutine &main::max called at ./pm_1155832_cond_use_mod.pl line 11.

Max is 2

##</code><code>##

$ PM_1155832_USE=1 pm_1155832_cond_use_mod.pl
Check for List::Util::max() at compile time
Max is 2