Hi.
On Tue, Jun 21, 2011 at 10:38 AM, Christopher Howard
What is a "unit numeric type pattern", as in the error: "Only unit numeric type pattern is valid". I can cause this error by mixing numbers into type definitions. And, therefore, I know how to avoid this error. But the error indicates that there /is/ such a thing as "valid" "unit numeric type pattern", and consequently I am quite curious as to what a such a thing is and what it would look like in code.
It's a hack (and I believe one that can soon be deprecated). It allows the number "1" to be used as a type, which is then interpreted as being isomorphic to GHC.Generics.Unit. Any other number in a type will produce the strange error you just mentioned. So this is syntactic sugar that has been added to support a particular language extension for generic deriving. I think the new generic deriving mechanism currently being implemented by Pedro doesn't rely/benefit from nicer syntax for the unit type. So this could be removed soon, and free up the syntax for something like type-level naturals. Cheers, Andres