(2) You are parsing strictly, meaning you have to read the whole input file before anything can be output.
This is likely the main performance problem. I'm guessing you are using parsec. Try switching to polyparse if you want to try out lazy parser combinators instead. (module Text.ParserCombinators.Poly.Lazy) http://www.cs.york.ac.uk/fp/polyparse/ There are other incremental parsers out there too, although they may be more complicated because they solve a larger problem: http://yi-editor.blogspot.com/2008/11/incremental-parsing-in-yi.html
I also suspect that manyTill is a really bad choice, since it doesn't give you anything until the end token.
This is not an "also" - it is the same problem of too much strictness. Polyparse's combinator 'manyFinally' is the corresponding combinator that works lazily if you want it to. Regards, Malcolm