> The restriction on the currying of type synonyms is therefore
> a semantic restriction on types, not just a syntactic restriction on
> type expressions.
Exactly. But I don't think we need to complicate the kind
system by having special kinds for type synonyms.
In fact type synonyms can be said to have no deeper meaning at all.
They can all be expanded out by simple substitution, and the rules
for how they are formed and used makes sure this is possible.
I've always viewed them as a (sane) form of macros that do not
really need to be explained in the semantics. (That's why I
worry when people suggest that Haskell should allow recursive type
synonyms.)
-- Lennart
