> Packrat isn't really a parsing algorithm - the PEG is the parsing algorithm.
The way I've seen it presented, PEG is primarily a style of grammar (basically, prioritized choice instead of normal alternation) and Packrat is a parsing algorithm.
The way I've seen it presented, PEG is primarily a style of grammar (basically, prioritized choice instead of normal alternation) and Packrat is a parsing algorithm.
A PEG is imperative. It's already an 'algorithm' and already describes how to parse it. That's different to traditional declarative grammars that people are used to, which need an algorithm to go with the grammar.
Or alternatively you could claim no CFG needs an algorithm either, since you could just use recursive descent on everything...
You don't need an extra algorithm to parse. You'd just like one to make sure it runs reasonably fast.
You can't use recursive descent on everything - how do you build a reclusive descent parser for an ambiguous grammar? You'd have to introduce some extra rules. That's the parsing algorithm, distinct from the grammar.
I think you can probably also use GLR (or whatever) to parse a language described by a PEG too. All you should need to do is to just prune the extra branches. If I'm not mistaken it should get you a better worst-case complexity than Packrat too. So I really don't see how you can say PEG is an algorithm... you have plenty of options for what algorithm to use, it's just that people prefer a particular one.