use strict;
my $OS_TYPE = $^O eq 'MSWin32' ? 'win' :
              ($^O eq 'nonstop_kernel' ? 'nsk' : 'unix');
sub win_fn  { print "windows version of function\n" }
sub nsk_fn  { print "nsk version of function\n"     }
sub unix_fn { print "unix version of function\n"    }
my %xplat = (
    'win'  => \&win_fn,
    'nsk'  => \&nsk_fn,
    'unix' => \&unix_fn,
);
sub xplatform_fn { return $xplat{$OS_TYPE}->() }
xplatform_fn();