I sent this to haskell-cafe a little while ago but didn't get a response, so I thought I'd try here. I'd guess this is a case of the GHC user guide needing an update, but I'd like an expert opinion. --- According to sections 7.4.3 and 7.4.4 of the latest GHC documentation https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/data-type-ex... you can define (7.4.3) an infix type constructor as long as it begins with a colon, for example data a :*: b = Foo a b and furthermore (7.4.4) you can define an infix operator without having to use a colon if you enable the TypeOperators extension: data a * b = Foo a b However if I try the former without using TypeOperators I get this compiler error in 7.10.2: Illegal declaration of a type or class operator ‘:*:’ Use TypeOperators to declare operators in type and declarations Using TypeOperators fixes this, but then * without colon also works so I don't see the point of using colon anymore. My guess is this was some some kind of historical distinction which is no longer valid and the documentation needs to be updated. Is this true, or am I missing something? John