###
### dir_walk_curried
###

## Chapter 7 section 2.4

 sub dir_walk {
  unshift @_, undef if @_ < 3;
  my ($top, $filefunc, $dirfunc) = @_;

  my $r;
  $r = sub {
    my $DIR;
    my $top = shift;
    if (-d $top) {
      my $file;
      unless (opendir $DIR, $top) {
        warn "Couldn't open directory $code: $!; skipping.\n";
        return;
      }

      my @results;
      while ($file = readdir $DIR) {
        next if $file eq '.' || $file eq '..';
        push @results, $r->("$top/$file");
      }
      return $dirfunc->($top, @results);
    } else {
      return $filefunc->($top);
    }
  };
  defined($top) ? $r->($top) : $r;
}