Hello, I've been attempting to use GADTs to create a small domain specific language, and I'm running into an odd problem. Adding one case to the example at the beginning of the Wobbly types paper: data Term :: * -> * where Lit :: a -> Term a Inc :: Term Int -> Term Int IsZ :: Num a => Term a -> Term Bool Div :: Fractional a => Term a -> Term a -> Term a If :: Term Bool -> Term a -> Term a -> Term a and extending the eval function accordingly: eval :: Term a -> a eval (Lit i) = i eval (Inc t) = eval t + 1 eval (IsZ t) = eval t == 0 eval (Div t u) = eval t / eval u eval (If cond cons alt) = if eval cond then eval cons else eval alt I get an error "No instance for (Fractional a) arising from the use of '/'" This seems odd to me, since Div is constrained to have fractional arguments. Is there something obvious I'm missing? Thanks, /g