Combinators for ReadP
Malcolm.Wallace at cs.york.ac.uk
Mon Jul 26 06:00:31 EDT 2004
John Meacham <john at repetae.net> 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 <msjogren at gmail.com> 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
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