[Haskell-cafe] A very nontrivial parser

Jonathan Cast jcast at ou.edu
Sun Jul 8 14:01:06 EDT 2007

On Sunday 08 July 2007, Andrew Coppin wrote:
> Jonathan Cast wrote:
> > I think surely you're using existential data types rather than rank-2
> > types.
> You expect *me* to know?

Surely not :)  That's why I tried briefly explaining the ideas again.

> > Existential types: each application of Encoder2 is to arguments which
> > require a specific value of x.
> >
> > Rank-2 types (polymorphic fields, actually): each application of Encoder2
> > is to arguments which work with any value of x.
> All I know is it didn't compile, so I added {-# LANGUAGE Rank2Types #-},
> and now it works. *shrugs*

If  you're happy, then I guess I can accept the situation.  I think you'll 
trip over the distinction again, but that's just me.

Jonathan Cast

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