consumer(3)
NAME
Parse::RecDescent::Consumer - reveal text matched through
n token transitions.
SYNOPSIS
use Parse::RecDescent::Consumer;
# then in a Parse::RecDescent grammar...
url: <rulevar: $C> url: { $C = Consumer($text) } httpurl {
REBOL::url->new(value => $C->($text)) }
| { $C = Consumer($text) } ftpurl {
REBOL::url->new(value => $C->($text)) }
DESCRIPTION
A common need when writing grammars is to know how much
text was consumed at different points in a parse. Usually,
this involves a lot of brain-twisting unwinding of of
highly nested list-of-lists (of lists...). Instead this
module allows you to take the low-road approach. You sim
ply create a "Consumer" which records the current text
about to be parsed.
After you have successfully transitioned through the
desired tokens, you simply re-call your "Consumer" and it
gives you the text that was consumed during the token
transitions without you having to unravel a highly nested
list-of-lists (of lists...).
IMPLEMENTATION
- when you first call Consumer(), you are returned a closure
which has the current text remaining to be parsed in it.
When you evaluate the closure, passing it the (more or
less consumed) new text, the closure calculates the dif
ference in length between the two texts, and returns a
substring of the first equating to the amount of text con
sumed between calls: - sub Parse::RecDescent::Consumer {
my $text=shift;
my $closure = sub {my $new_length=length($_[0]);
my $original_text = $text;
my $original_length = length($text);
return substr($original_text, 0, ($original_length-$new_length));} - }
- EXPORT
- None by default.
AUTHOR
T. M. Brannon, <tbone@cpan.org>