Parse::RecDescent matches well with the way a lot of people think about parsing, which is one of the reasons it's so popular, I think. (That and the fact that Damian writes darned good software) Unfortunately recursive descent parsing is just darned slow in general, so we can't use it for Parrot's parser.

Parrot's parser will likely be more like the classic parsing tools. They're classic because they work and work quickly, and this is one of the places where programmer convenience will get sacrificed for speed.