#!pil

=pod

=head1 DESCRIPTION

This is a very simple numeric range implemeted as 
a functional lazy stream. The head of the stream 
is a value, and the tail is another lazy stream 
which will return the next element in the stream 
until the stream is exhausted, at which point it
will return nil.

This also supports infinite streams as well, if 
you pass in nil as the $end parameter, it will
go on forever. 

=head1 AUTHOR

Stevan Little <stevan@iinteractive.com>

=cut

&num_range := -> $start, $end {
	-> {
		[ $start, 
		  $start`eq($end)`if_else(
		  	  -> { nil },
			  -> { &num_range`($start`increment(), $end) }
		)]
	};
};

&head := -> &range { &range`()`fetch(0) };
&tail := -> &range { &range`()`fetch(1) };

&show := -> &r {
	&redo := &?SUB;
	&head`(&r)`trace();
	&tail`(&r)`is_nil()`if_else(
		-> { nil },
		-> { &redo`(&tail`(&r)) }
	)
};

&show`(&num_range`(0, 10));

# Uncomment below for an infinite stream.
# By passing nil in as the $end parameter,
# then we get an infinite range since $start
# will never match nil :)
# &show`(&num_range`(1, nil));