14 May
2018
14 May
'18
8:15 a.m.
Dear List, Chapter 14 of LYH appears to suggest that a Just value can be added to an Int. Quote from http://learnyouahaskell.com/for-a-few-monads-more#useful-monadic-functions "For instance, say we have Just 9 and the function \x -> Just (x+1). If we map this function over Just 9, we're left with Just (Just 10)." I've tried the following in ghci but got the error: <interactive>:12:1: error: • Non type-variable argument in the constraint: Num (Maybe a) (Use FlexibleContexts to permit this) • When checking the inferred type it :: forall a. (Num (Maybe a), Num a) => Maybe a Am I reading the quote wrong? Is Just (Just 10) a hypothetical? Regards, - Olumide