[Haskell-cafe] Is there Functor instance of Enumerator'
alex.solla at gmail.com
Fri Jul 1 19:44:46 CEST 2011
On Fri, Jul 1, 2011 at 7:38 AM, yi huang <yi.codeplayer at gmail.com> wrote:
> Say i want to compose Enumerator ByteString m b and Iteratee Builder
> m b, so I try to transform the enum to Enumerator Builder m b,
> providing function ByteString -> Builder. It's like implement a
> Functor instance for Enumerator. But i failed, there are no way to
> make type system happy.
> Am I right that there is no Functor instance of Enumerator?
I'm pretty sure there is one, but it's a functor over b. So something like:
instance Functor (Enumerator a m)
I think you want to use an Enumeratee:
enumerateeByteStringBuilder :: Enumeratee ByteString Builder m b
Check out map :: (a -> b) -> Enumeratee a b m c
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