J. Garrett Morris writes:

Hello,

I'm attempting to use GADTs for the first time, and I'm running into an (I think) odd error. My file includes:

data DFExpr :: * -> * where Deriv :: (Num t) => t -> Deriv Int (DFExpr t) (DFExpr t)

I think you want something like this: Deriv :: Int -> DFExpr t -> DFExpr t -> DFExpr t Ignorning the other clauses, it's equivalent to data DFExpr t = Deriv Int (DFExpr t) (DFExpr t) -- David Menendez | "In this house, we obey the laws http://www.eyrie.org/~zednenem | of thermodynamics!"