P.S. Question for merlyn if he checks back: What is the nibbling approach? I performed a search here and looked through my library, but couldn't find anything ....
Nibbling is a method of tokenization by constantly attempting substitutions at the beginning of the string, replacing it with nothing if found. 
$_ = "Hello there, people!";
@output = ();
while (length) {
  (push @output, "word: $1"), next if s/^(\w+)//;
  (push @output, "spaces"), next if s/^\s+//;
  (push @output, "punc: $1"), next if s/^(.)//;
  die "how did I get here?";
}
print map "$_\n", @output;

[download]
This is fine for small strings, but the constant leftward shuffling of the string gets very expensive for huge strings. P::RD uses nibbling. P::FastDescent will use pos() scanning instead: 
$_ = "Hello there, people!";
@output = ();
while (pos $_ <= length $_) {
  (push @output, "word: $1"), next if /\G(\w+)/gc;
  (push @output, "spaces"), next if /\G\s+/gc;
  (push @output, "punc: $1"), next if /\G(.)/gc;
  die "how did I get here?";
}
print map "$_\n", @output;

[download]
Much easier, but wasn't available when theDamian first wrote P::RD.

-- Randal L. Schwartz, Perl hacker

In reply to Nibbling Approach (was Re: Re: Parse::RecDescent size limit?) by merlyn
in thread Parse::RecDescent size limit? by Anonymous Monk

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