Generate wildcard type parameters by janmasrovira · Pull Request #200 · haskell-effectful/effectful

janmasrovira · 2024-02-13T15:47:20Z

Consider the following code:

data Output (o :: GHC.Type) :: Effect where
  Output :: o -> Output o m ()

makeEffect ''Output

Compiling this with warnings turned on generates the following warning:

warning: [GHC-40910] [-Wunused-type-patterns]
    Defined but not used on the right hand side: type variable ‘o’
   |
12 | makeEffect ''Output

This is because the generated definition looks like this:

type instance DispatchOf (Output o) = 'Dynamic

And the variable o is not used in the rhs.

To fix this, I've substituted all type variables with wildcard, so the generated code would look like this instead:

type instance DispatchOf (Output _) = 'Dynamic

arybczak · 2024-02-13T21:37:02Z

Thanks. Please add an appropriate changelog entry to effectful-th.

janmasrovira · 2024-02-13T23:40:08Z

done

Generate wildcard type parameters

69e6102

add changelog item

1841410

arybczak merged commit 2037be9 into haskell-effectful:master Feb 14, 2024

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