Really? fully lazy parsers are notoriously tricky, which parsing library do you use? I have been told that its lazy in that respect, I've never actually checked. As for the parsing library, its an entirely arbitrary one :) Its not monadic, its really really old, and its in the Yhc repo under src/compiler98/Parse. I don't have a clue how it works...
I keep wanting to switch jhc to packrat parsing http://pdos.csail.mit.edu/~baford/packrat/ I've seen that, but I want to switch Yhc to: http://www-users.cs.york.ac.uk/~ndm/projects/parsing.php (O(n), super-duper fast, no shift/reduce nonsense, easy to specify)
I prefer pre-generated parsers - you can always parse the additional syntax and then tell the user what flag that have to enable to get it to actually work. Thanks Neil