[Haskell-cafe] Is there Functor instance of Enumerator'

[yi huang]

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?

--
http://www.yi-programmer.com/blog/

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[Alexander Solla]

On Fri, Jul 1, 2011 at 7:38 AM, yi huang <yi.cod...@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

http://hackage.haskell.org/packages/archive/enumerator/0.4.0.1/doc/html/Data-Enumerator.html#v:map