Re: Parse::RecDescent and need for speed

Personally, I find that code generated by Parse::RecDescent is generally slower than a hand-coded recursive descent parser. But such comparisons really depend on the skill of the programmer.

Without seeing your language, grammar, or parser, I can't give any specific advice. In perl top-down parsers, nonterminals in your grammar generally correspond to functions and terminals to regular expressions. So eating comments should be a pretty fast operation. An excellent book on parsers and compilers is Compilers: Principles, Techniques, and Tools, by Aho, Sethi and Ullman.

-Mark

Comment on Re: Parse::RecDescent and need for speed

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Re^2: Parse::RecDescent and need for speed by merlyn (Sage) on Feb 16, 2005 at 01:03 UTC
Also, keep in mind that Parse::RecDescent parses by "nibbling", which is very expensive for large strings. At one point, theDamian said he would rewrite it to use pos (which wasn't available in 5.004 when he wrote PRD), but has since gotten distracted by other things. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^3: Parse::RecDescent and need for speed by Anonymous Monk on Feb 16, 2005 at 10:11 UTC
At one point, theDamian said he would rewrite it to use pos (which wasn't available in 5.004 when he wrote PRD) Bull. `pos` was available in 5.000, as the perl5.000 manual will tell you.	[reply]
Re^4: Parse::RecDescent and need for speed by merlyn (Sage) on Feb 16, 2005 at 13:36 UTC
Mis-remembered. It's about pos(), but not pos(). What got added in 5.005 was m//gc, so a failed match didn't reset pos(). -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^5: Parse::RecDescent and need for speed by Anonymous Monk on Feb 16, 2005 at 14:41 UTC
Re^6: Parse::RecDescent and need for speed by merlyn (Sage) on Feb 16, 2005 at 15:04 UTC
Re^3: Parse::RecDescent and need for speed by Anonymous Monk on Feb 16, 2005 at 16:38 UTC
At one point, theDamian said he would rewrite it to use pos (which wasn't available in 5.004 when he wrote PRD) First non-comment, non-whitespace line of Parse::RecDescent: `use 5.005;` [download]	[reply] [d/l]
Re^4: Parse::RecDescent and need for speed by merlyn (Sage) on Feb 16, 2005 at 17:49 UTC
In fact, the original was written for 5.004, because it was written on MacPerl, which was only 5.004 at the time. The use 5.005 was no doubt added later when some other feature required 5.005. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]