An Idea to Handle Left-Recursion in Parsing Expression Grammars (2010)

> It should be noted that while Packrat parsing obviously adds an extra layer of complexity over ‘pure’ PEGs, contrary to expectations it often slows parsing down when used blindly for every rule.

Especially these days, and really definitely in a lot of dynamic languages (cfe Ruby), the kind of allocation rate that packrat parsing produces has a significantly negative effect on performance. Applied blindly you're just trading n^2 performance for n^2 memory use, and that may not work out the way you think it should.