package ChainComparable;

use strict;

use UNIVERSAL ();


sub new {
	my $class = shift;
	
	# allow for returning either a list or a scalar
	return wantarray
		? (map { my $i = $_; bless \$i, $class } @_)
		: (bless \shift, $class);
}


sub comparison {
	# whee, currying
	
	my $sub = shift;
	
	return sub {
		my ($a, $b, $swap) = @_;
		
		$a = $$a;
		
		# allow for comparisons between two instances of this class
		$b = $$b if UNIVERSAL::isa($b, __PACKAGE__);
		
		# put the args in the right order
		($a, $b) = ($b, $a) if $swap;
		
		if (defined $a and $sub->($a, $b)) {
			if ($b != 0) { return __PACKAGE__->new($b)           }
			else         { return __PACKAGE__->new("0 but true") }
		}
		else { return __PACKAGE__->new(undef) }
	};
}


use overload (
	bool  => sub { $$_[0] },
	'""'  => sub { $$_[0] },
	"0+"  => sub { $$_[0] },
	
	"==" => comparison(sub { $_[0] == $_[1] }),
	"!=" => comparison(sub { $_[0] != $_[1] }),
	"<<" => comparison(sub { $_[0] <  $_[1] }),
	">>" => comparison(sub { $_[0] >  $_[1] }),
);