Generalize with MonadAff

[Joop Ringelberg]

I have a question about generalizing. Starting with this function:

  test0 :: String -> String

  test0 s = s

we can generalize it in its argument:

  test1 :: forall a. Show a => a -> String

  test1 s = show s

or in its functional result:

  test12 :: forall a. Show a => String -> a

  test12 s = s

Now consider the following function:

  test2 :: forall e. Aff e Int

  test2 s = pure 0

I would like to generalize it in its functional result:

  test3 :: forall e m. MonadAff e m => m e Int

  test3 s = pure 0

However, I now get an error:

Could not match kind type with kind # Control.Monad.Eff.Effect while checking the kind of MonadAff e m => m e Int in value declaration test3.

I cannot understand why. Moreover, I've found an example of similar such generalizing in Hyper.Node.Server, for example in this type:

    write :: forall m e. MonadAff e m => Buffer -> NodeResponse m e

[Alex Berg]

Sorry, don't have an environment with PS compiler available, but did try this? The `e` is part of MonadAff and describes the single `m`, so don't need to include `e` there in `m e Int`.

test3: forall e m. MonadAff e m => m Int

test3 s = pure 0

[Joop Ringelberg]

You are quite right! However, I still find an issue with the expressions. Only if I change the type so it actually includes a functional argument, the compiler accepts it:

  test3 :: forall e m. MonadAff e m => Int -> m Int

  test3 = pure

Thank you very much for clarifying this point.

Joop