Re: [Haskell-cafe] "mapping" an Enumerator

Michael Snoyman wrote:

On Wed, Dec 21, 2011 at 12:35 PM, Kannan Goundan 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

I tried something like that but the resulting type isn't quite what I'm looking for. mapEnum :: Monad m => (a -> b) -> Enumerator a m (Step b m r) -> Enumerator a m r (BTW, Michael, my exact use case is that I have ByteString enumerators, but your HTTP-Enumerator library wants Blaze.Builder enumerators :-)