sub _findPaths2 {
    my( $code, $graph, $start, $end, $path, $seen ) = @_;
    return $code->( @$path, $end ) if $start eq $end;
    $seen->{ $start } = 1;
    for ( grep !$seen->{ $_ }, @{ $graph->{ $start } } ) {
        _findPaths2( $code, $graph, $_, $end, [ @$path, $start ], { %$seen } ),
    }
}
sub findPaths2(&@) { _findPaths2( @_, [], {} ); }

findPaths2{
    print join ' ', @_;
} \%graph, $start, $end;