[Haskell-cafe] A very nontrivial parser

[Andrew Coppin]

Jonathan Cast wrote:
> I think surely you're using existential data types rather than rank-2 types.
>   

You expect *me* to know?

> 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*