On Saturday, 7 July 2012 at 09:06:57 UTC, Roman D. Boiko wrote:
http://stackoverflow.com/questions/11373644/performance-of-parsers-peg-vs-lalr1-or-llk
So far it looks like LALR parsers may have lower constant factors than Packrat.
The difference could be minimized by paying attention to parsing of terminal symbols, which was in my plans already. It is not necessary to strictly follow Packrat parsing algorithm.
The benefits of Pegged, in my view, are its support of Parsing Expression Grammar (PEG) and compile-time evaluation. It is easily extensible and modifiable.
When I implemented recursive-descent parser by hand in one of early drafts of DCT, I strongly felt the need to generalize code in a way which in retrospect I would call PEG-like. The structure of my hand-written recursive-descent parser was a one-to-one mapping to an implemented subset of D specification, and I considered it problematic, because it was needed to duplicate the same structure in the resulting AST.
PEG is basically a language that describes both, the implementation of parser, and the language syntax. It greatly reduces implicit code duplication.
I think that generated code can be made almost as fast as a hand-written parser for a particular language (probably, a few percent slower). Especially if that language is similar to D (context-free, with fine-grained hierarchical grammar). Optimizations might require to forget about strictly following any theoretical algorithm, but that should be OK.
