Fast Haskell Parser

[John D. Earle]

Simon Marlow: Personally I find Parsec and the other parser combinator 
libraries quite difficult to use when it comes to deciding where to put 
'try'; ReadP is the exception here, because it does general backtracking and 
doesn't make you decide where to use 'try'.

John D. Earle: I bet this has something to do with lazy verses strict 
evaluation. ReadP alleviates the problem by doing the work for you. Lazy 
evaluation fits nicely with the aims of high level language design. Lazy 
evaluation gives more opportunities for a compiler to optimize the code 
using non-domain specific optimizations. At some point in the compilation 
process lazy becomes strict. When designing domain specific optimizations 
you are working on the low level details at around the lazy-strict 
transition boundary, however. Part of the problem appears to be that I do 
not understand how to selectively carry out strict evaluation in Haskell. 
Lazy evaluation is the default.