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How to specialize mapM for IO in Haskell

Say I have a task that represents some computation from k to v where some inputs have to be fetched externally.

k

v

newtype Task k v = Task { run ∷ ∀ f. Monad f ⇒ (k → f v) → f v }


For some tasks mapM will be used, e.g. to fetch multiple keys. I want to specialize mapM for some monads. Specifically for the IO monad I want to use Control.Concurrent.Async.mapConcurrently to perform actions concurrently.

mapM

mapM

IO

Control.Concurrent.Async.mapConcurrently

My first instinct is to introduce a wrapper type

newtype AsyncIO a = AsyncIO { io :: IO a }


and then introduce

instance Monad AsyncIO


However this doesn't work because in the current GHC implementation mapM is defined in term of traverse, which is in Traversable.

mapM

traverse

Traversable

Is there an elegant solution for this?

mapM

Task

1 Answer
1

Have run take mapM or mapConcurrently as an additional argument, or for possibly less passing as an implicit parameter, though I'm not sure whether the latter will clash with f's quantification.

mapM

mapConcurrently

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