Not an issue - just a question about the haskell type system that came to my mind by looking at data-fix

[alaendle]

Please excuse if this is a dumb question 😃

Maybe I just missing some special Haskell syntax - but I don't find a good explanation for:

type MyMaybe :: Type -> Type
type MyMaybe = Maybe

type MyMaybe' :: Type -> Type
type MyMaybe' a = Maybe a

type Works = Fix MyMaybe

-- • The type synonym ‘MyMaybe'’ should have 1 argument, but has been given none
-- • In the type synonym declaration for ‘DoesntWork’
type DoesntWork = Fix MyMaybe'

Here for sure the argument can be avoided - but what if the type is nested - e.g. something like Either (Maybe a ) ()? How to apply Fix in such a case?

[anton-k]

In Haskell we can not use type-synonyms as functions from type to type. A type synonym should always be fully applied.
You can solve it by declaring the new datatype (using data or newtype).

[alaendle]

Thanks!