[Haskell-cafe] "mapping" an Enumerator

[Michael Snoyman]

On Wed, Dec 21, 2011 at 12:35 PM, Kannan Goundan <kannan at cakoose.com> wrote:
> I'm using the Data.Enumerator library.  I'm trying to write a "map"
> function that converts an Enumerator of one type to another.
> Something like:
>
>   mapEnum :: Monad m =>
>          (a -> b) ->
>          Enumerator a m r ->
>          Enumerator b m r
>
> Any hints?
>
> (My exact use case is that I have a ByteString enumerator and I
> need to pass it to something that requires a Blaze.Builder
> enumerator.)
>
>
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You can use the Data.Enumerator.List.map function to create an
Enumeratee, and then the Data.Enumerator.$= operators to join them
together. Something like:

mapEnum f enum = enum $= EL.map f