[Haskell-cafe] Re: The Proliferation of List-Like Types
jgoerzen at complete.org
Wed Feb 20 11:28:16 EST 2008
On 2008-02-20, John Goerzen <jgoerzen at complete.org> wrote:
> I notice that Data.Foldable does some similar things but does not use
> multi-parameter type classes. I seem to recall that I attempted to do
> this in the same manner, but got tripped up somewhere. I can't
> remember now exactly what the problem was, but I can go back and look
> if nobody knows off-hand.
I went back and looked.
The problem is that ByteString doesn't work as a member of Foldable,
or of ListLike without it being MPTC. Trying to do so yields:
Expected kind `* -> *', but `BS.ByteString' has kind `*'
In the instance declaration for `F.Foldable BS.ByteString'
Is there any way around that, other than MPTC?
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