* Merijn Verstraaten
2) for some reason the type families syntax always requires a full argument list, which I find rather ugly. I would much prefer to use KindSignatures and write "type family Restrict :: * -> [*] -> Constraint", but GHC does not allow this. Is there a specific reason for not allowing this syntax?
I believe this is done to simplify (or even enable) type inference. This is similar to the situation with type synonyms. type M1 = Maybe is different from type M2 a = Maybe a in that M1 has kind * -> *, while M2 is not a type constructor and doesn't have a kind — but when applied to a type of kind * it expands to a type of kind *. The same with the type families. You can define type families that return e.g. [*] -> *, but then you cannot pattern match on the [*] type argument. If you could, that would be equivalent to type-level lambdas, and that would make type inference hard or impossible. Roman