#! /usr/bin/perl

use strict;
use warnings;

my $f = sub {
  return @_ == 1
    ? undef
    : ( [ splice @_, -2 ], @_ == 1 ? () : &{ $_[0] }(@_) );
};
map { print "$_->[0] -> $_->[1]\n" }
  $f->( $f, %{ { x => 5, y => 8, z => 42 } } );