use strict;
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"    }
sub xplatform_fn {
    if ($^O eq 'MSWin32') {
        return win_fn();
    } elsif ($^O eq 'nonstop_kernel') {
        return nsk_fn();
    } else {
        return unix_fn();
    }
}
xplatform_fn();