Singular Type Constructor

30 Jul 2001

      Consider:

--
data T a = T
--

Is there anything in the Prelude or a standard library that looks like 
this? Should there be? What should it be called? 'Singleton'? 'Reified'? 
'T'?

I looked but couldn't find anything. Such a simple type constructor is in 
fact very useful when you need to pass types around to disambiguate class 
instances. For instance:

--
class HasTypeName t where
		getTypeName		:: T t -> String

instance HasTypeName Int where
		getTypeName T = "Int"

instance HasTypeName () where
		getTypeName T = "()"

intName = getTypeName (T :: T Int)
--

-- 
Ashley Yakeley, Seattle WA