Re: [Haskell-cafe] Why this doesn't type checked

On 6/27/10 21:52, Victor Nazarov wrote:

...

class Sizeable sizeable where type Sizeof sizeable sizeof :: Sizeof sizeable

This is where the type checker should complain. There is no valid way to call sizeof, regardless of what instances are available. The situation is similar to this:

class C a where x :: Int

In which case the compiler says:

The class method `x' mentions none of the type variables of the class C a When checking the class method: x :: Int In the class declaration for `C'

I thought there was already a trac ticket for this, but I can't find it right now. Martijn.