Re: Combinators for ReadP

John Meacham writes:

possible to use ReadP as a simple standard (as in comes with the libraries) very lightweight parsing monad

Errm, "comes with the libraries" does not necessarily make it standard. As the file header says, Text.ParserCombinators.ReadP is non-portable because it uses local universal quantification. Martin Sjögren writes:

While we're discussing changes, is there an overwhelmingly good reason for the use of local quantification beyond making the type signatures simpler? Writing newtype ReadP r a = R ((a -> P r) -> P r) (like in ContT) would make ReadP completely Haskell98 as far as I can tell.

I think you'll find that without the local universal quantifier, you cannot make ReadP a (useful) instance of Monad, because your 'r' parameter would be fixed across >>=, whereas it really needs to be variable. Regards, Malcolm