[Haskell-beginners] What is wrong with my types signatures.

[PICCA Frederic-Emmanuel]

Thanks a lot.

> Here's my guess.  I can't be sure without class instances and some
> function types that are not in code.

> sh' <- lift $ runMaybeT $ shapeND d :: Pipe a (XrdMeshFrame sh) IO (Maybe sh?)
...

> f <- lift $ runMaybeT $ rowND d (fromIndex sh' i') -- <- sh' is (Maybe
> sh), guessing that fromIndex does not take a Maybe.

This was the problem.

Thanks.

PS: The error message was right (as usual :), but I do not know why I was not able to found the cuprite.