nested list comprehension [Perl] [プログラム]

http://codepad.org/f2DsjilG

sub _comprehend_list_inner
{
  my @pairs = @_;
  my $dim = pop @pairs;
  my $cond_sub = pop @pairs;

  if (@pairs) {
    my ($start, $end) = splice @pairs, -2;
    my $next_sub = sub {
      my @list_ = @_;
      my $result_ = pop @list_;
      for my $i ( $start .. $end ) {
        my @next_list_ = @list_;
        push @next_list_, $i;
        push(@$result_, \@next_list_)
          if $cond_sub->(@next_list_, (@next_list_  $dim ? () : $result_)) &&
             @next_list_  $dim;
      }
      return @$result_;
    };
    return _comprehend_list_inner(@pairs, $next_sub, $dim);
  }

  # no pairs
  my $result_ = [];
  return $cond_sub->($result_);
}

sub comprehend_list
{
  my @pairs = @_;
  my $cond_sub = do {
    if ( ref($pairs[$#pairs]) =~ /^CODE/ ) {
      pop @pairs;
    }
    else {
      sub { 1 };
    }
  };
  die "ranges are not pairs" if (@pairs % 2);

  my $pairs_cnt = @pairs / 2;

  return _comprehend_list_inner(@pairs, $cond_sub, $pairs_cnt);
}

use Data::Dumper;
local $Data::Dumper::Terse = 1;
local $Data::Dumper::Indent = 0;

print Dumper(
  comprehend_list(
    0 => 9,
    0 => 9,
    sub { $_[0] + $_[1] == 5 && $_[0] > $_[1] }
  )
), "\n";
print Dumper(
  comprehend_list(
    0 => 4,
    0 => 4,
  )
);

普段curry化とか使わないから、若干頭がこんがらがってみたり..