Simon, Regarding the note you attached to the Trac ticket on the pretty-printing of kind ascriptions (http://hackage.haskell.org/trac/ghc/ticket/5141#comment:2):

Note, though, that it's likely that we're considering making operators like '*' into type ''constructors'' rather that type ''variables'. This is inconsitent with terms, but is jolly convenient: {{{ data a + b = Left a | Right b }}} Of course there'll be a flag. But let us know if you think that having operators be type variables is very useful. (I tend to think it's more confusing than useful.)

I myself am perfectly alright with being "forced" to write {{{ data a :+: b = Left a | Right b }}} Although I don't have a *convincing* example of the usefulness of operators as type variables, I like the idea of consistency with the term level: IMO it keeps things predictable. And even as it may not qualify as convincing, I do remember having written code similar to {{{ data (f :+: g) a = Inl (f a) | Inr (g a) data (f :*: g) a = f a :*: g a class FunctorOp ((&) :: (* -> *) -> (* -> *) -> (* -> *)) where ... instance FunctorOp (:+:) where ... instance FunctorOp (:*:) where ... class FunctorOp (&) => CommOp (&) where comm :: f & g -> g & f instance CommOp (:+:) where ... instance CommOp (:*:) where ... f :: (CommOp (&), Functor f, Functor g) -> f & g -> ... f ... = ... }}} All this, of course, just to put in my tuppence worth. Cheers, Stefan