In my experience* , PEGs are really good for basic parsing (from basics to a few steps beyond advanced Perl regex hackery), but aren't really a complete substitute for other formal parsing methods. Having separate lexing and parsing phases can make things cleaner, because the grammar no longer has to keep track of purely lexical details like whitespace. PEGs are simple and easy to build interactively, though, so they occupy a very useful middle ground. I'm surprised they aren't more popular.
My experience with really large scale grammars is extremely limited so it's good to hear your thoughts on that!
My main issue so far with PEGs is that the generators seem to produce parsers that are relatively slow. That being said I need to experiment with PEGs in languages other than Ruby. Thanks!
LPEG is actually quite fast. (Often as fast or faster than well-tuned regexp implementations.)
In general, Lua is usually faster than Ruby and JS because the language itself seems to have been engineered with a very clear understanding of where the language could be expressive/dynamic without unnecessarily sacrificing efficiency, and it's had a long time to mature. LPEG was written by one of the primary Lua authors, and it shows.
If you're geeked about PEGs, I highly recommend reading the paper and then the source. There are some details specific to the Lua C API, but it shouldn't be that hard to port or understand in isolation.
Comments
In my experience* , PEGs are really good for basic parsing (from basics to a few steps beyond advanced Perl regex hackery), but aren't really a complete substitute for other formal parsing methods. Having separate lexing and parsing phases can make things cleaner, because the grammar no longer has to keep track of purely lexical details like whitespace. PEGs are simple and easy to build interactively, though, so they occupy a very useful middle ground. I'm surprised they aren't more popular.
* I haven't used Treetop or PEG.js, but I've done a lot with Lua's LPEG (http://www.inf.puc-rio.br/~roberto/lpeg/lpeg.html), which is based on the same formalism.
My experience with really large scale grammars is extremely limited so it's good to hear your thoughts on that!
My main issue so far with PEGs is that the generators seem to produce parsers that are relatively slow. That being said I need to experiment with PEGs in languages other than Ruby. Thanks!
LPEG is actually quite fast. (Often as fast or faster than well-tuned regexp implementations.)
In general, Lua is usually faster than Ruby and JS because the language itself seems to have been engineered with a very clear understanding of where the language could be expressive/dynamic without unnecessarily sacrificing efficiency, and it's had a long time to mature. LPEG was written by one of the primary Lua authors, and it shows.
If you're geeked about PEGs, I highly recommend reading the paper and then the source. There are some details specific to the Lua C API, but it shouldn't be that hard to port or understand in isolation.