How do I create something like a negated character class with a string instead of characters?
- by Chas. Owens
I am trying to write a tokenizer for Mustache in Perl. I can easily handle most of the tokens like this:
#!/usr/bin/perl
use strict;
use warnings;
my $comment = qr/ \G \{\{ ! (?<comment> .+? ) }} /xs;
my $variable = qr/ \G \{\{ (?<variable> .+? ) }} /xs;
my $text = qr/ \G (?<text> .+? ) (?= \{\{ | \z ) /xs;
my $tokens = qr/ $comment | $variable | $text /x;
my $s = do { local $/; <DATA> };
while ($s =~ /$tokens/g) {
my ($type) = keys %+;
(my $contents = $+{$type}) =~ s/\n/\\n/;
print "type [$type] contents [$contents]\n";
}
__DATA__
{{!this is a comment}}
Hi {{name}}, I like {{thing}}.
But I am running into trouble with the Set Delimiters directive:
#!/usr/bin/perl
use strict;
use warnings;
my $delimiters = qr/ \G \{\{ (?<start> .+? ) = [ ] = (?<end> .+?) }} /xs;
my $comment = qr/ \G \{\{ ! (?<comment> .+? ) }} /xs;
my $variable = qr/ \G \{\{ (?<variable> .+? ) }} /xs;
my $text = qr/ \G (?<text> .+? ) (?= \{\{ | \z ) /xs;
my $tokens = qr/ $comment | $delimiters | $variable | $text /x;
my $s = do { local $/; <DATA> };
while ($s =~ /$tokens/g) {
for my $type (keys %+) {
(my $contents = $+{$type}) =~ s/\n/\\n/;
print "type [$type] contents [$contents]\n";
}
}
__DATA__
{{!this is a comment}}
Hi {{name}}, I like {{thing}}.
{{(= =)}}
If I change it to
my $delimiters = qr/ \G \{\{ (?<start> [^{]+? ) = [ ] = (?<end> .+?) }} /xs;
It works fine, but the point of the Set Delimiters directive is to change the delimiters, so the code will wind up looking like
my $variable = qr/ \G $start (?<variable> .+? ) $end /xs;
And it is perfectly valid to say {{{== ==}}} (i.e. change the delimiters to {= and =}). What I want, but maybe not what I need, is the ability to say something like (?:not starting string)+?. I figure I am just going to have to give up being clean about it and drop code into the regex to force it to match only what I want. I am trying to avoid that for four reasons:
I don't think it is very clean.
It is marked as experimental.
I am not very familier with it (I think it comes down to (?{CODE}) and returning special values.
I am hoping someone knows some other exotic feature that I am not familiar with that fits the situation better (e.g. (?(condition)yes-pattern|no-pattern)).
Just to make things clear (I hope), I am trying to match a constant length starting delimiter followed by the shortest string that allows a match and does not contain the starting delimiter followed by a space followed by an equals sign followed by the shortest string that allows a match that ends with the ending delimiter.
