infix type constructors

I'm not sure how long this has been implemented in GHC, but I just noticed that infix type constructors are allowed, as in data a :- b = ... The syntactic asymmetry between type constructors and data contructors has bothered me for a while, so this is a welcome change! However, this syntax seems to be supported for "data" and "newtype" declarations, but not for "type" declarations. For example, type a :- b = ... does not seem to be allowed. Is there a reason for this? Or was it just an oversight? -- Chris