I managed to remove the Data.Reflection and Numeric.AD dependency entirely. In this case, Reverse is just a newtyped Num with a phantom variable added. Still, the same issue occurs. In one case the type gets defaulted to Integer if I try to pass a "forall a. Num a => t a -> a" to grad (which has type "Num a, Traversable t => (forall s. t (Reverse s a) -> Reverse s a) -> t a -> t a"). Then it complains that Integer isn't Reverse s a, and won't compile. In the other where I try to specifically pass the a value with type "forall s. t (Reverse s a) -> Reverse s a" it think the type variable would escape its scope, but I don't see why it should, or how to prevent that in the "doesnt3" example. I have no idea how to apply the fix used in the first two examples to the later two, or why it should even be necessary. -- View this message in context: http://haskell.1045720.n5.nabble.com/Type-error-depending-on-scope-of-patter... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.