use enum qw[ CODE GRAPH START PATH SEEN ];
sub _pathsFrom {
 _PATHSFROM:
  {
    return $_[CODE]->( @{ $_[PATH] }, $_[START] )
      unless exists $_[GRAPH]->{ $_[START] };
 
    for ( @{ $_[GRAPH]->{ $_[START] } } ) {
      if ( exists $_[SEEN]->{ $_[START] . "-$_" } ) {
        return $_[CODE]->( @{ $_[PATH] }, $_[START] );
      } else {
        @_=(
            @_[ CODE, GRAPH ], $_,
            [ @{ $_[PATH] }, $_[START] ], 
            { %{ $_[SEEN] }, $_[START] . "-$_", undef }
           );
        redo _PATHSFROM;
      }
    }
  }
}