parboiled

on where blocks are delimited by indentation level, the lexer needs to be hacked by hand (i.e. you have to cheat somewhere, because that's context-dependent and a bitch to deal with). In general, ANTLR generated parsers are more efficient and allow for certain hacks to be implemented easily, but PEG grammars are easier to write and allow for certain context-dependent rules that are very hard to implement in ANTLR. And PEG grammars need backtracking as an implementation detail and although memoization reduces the impact of that, the result will have less performance. Basically for quick prototypes I would choose PEG grammars and for industrial strength something like ANTLR. Btw, here's a cool Java/Scala library for creating PEG parsers, and it's much lighter and easier to setup than ANTLR: https://github.com/sirthias/parboiled/wiki And the syntax is basically Java/Scala: https://github.com/sirthias/parboiled/wiki/Simple-Java-Examp... AND the Scala way of defining grammars is so cool I can't even describe it - basically you can create new grammars by inheriting existing grammars - say you have a general SQL syntax that you want to specialize for MySQL / PostgreSQL. Works like a charm ;)