package Comp;

use strict qw( vars subs );
use warnings;

sub import
{
	my( $class, $file, $line ) = caller();

	#
	# comp { ... } ?VAR? => SUB, ...
	#
	my $comp;
	$comp = sub (&;@) {
		my( $sub, $var, $list, @x ) = @_;

		if ( my $r = ref($var) )
		{
			if ( $r eq 'CODE' )
			{
				push @x, $list;
				$list = $var;
				$var  = undef;
			} # if
			elsif ( $r ne 'SCALAR' )
			{
				die
"Neither a SCALAR nor a CODE reference in comp() in file '$file' at line $line.\n";
			} # elsif
		} # if
		else
		{
			$var = \${$class.'::'.$var};
		} # else

		my @l;

		for ( $list->() )
		{
			$$var = $_ if defined $var;
			push @l, @x ? $comp->( $sub, @x ) : $sub->();
		} # for

		return @l;
	};

	#
	# lcomp { ... } ?VAR? => LAZYSUB, ...
	#
	my $lcomp;
	$lcomp = sub (&;@) {
		my( $sub, $var, $list, @x ) = @_;

		if ( my $r = ref($var) )
		{
			if ( $r eq 'CODE' )
			{
				push @x, $list;
				$list = $var;
				$var  = undef;
			} # if
			elsif ( $r ne 'SCALAR' )
			{
				die
"Neither a SCALAR nor a CODE reference in comp() in file '$file' at line $line.\n";
			} # elsif
		} # if
		else
		{
			$var = \${$class.'::'.$var};
		} # else

		while ( defined( my $elem = $list->() ) )
		{
			$$var = $elem if defined $var;

			my($res) = @x ? $lcomp->( $sub, @x ) : $sub->();
			return $res if defined $res;
		} # for

		return undef;
	};

	#
	# lazy { ... } START
	#
	my $lazy = sub (&$) {
		my( $sub, $val ) = @_;

		my $start = $val;

		return sub{
			my($res) = $sub->(\$val);
			$val = $start if ! defined $res;
			return $res;
		};
	};

	*{$class.'::comp' } = $comp ;
	*{$class.'::lcomp'} = $lcomp;
	*{$class.'::lazy' } = $lazy ;
} # import

1;

__END__