Could not deduce (Show t)
haskell, typeclass
Solution
Class constraints on data types don't mean anything.
See this related question
Remove the constraint on the data type.
data Mat a = Mat {nexp :: Int, mat :: QT a}
deriving (Eq, Show)
Problem
I have this piece of code in Haskell that refuses to compile: ``` data (Eq a, Num a, Show a) => Mat a = Mat {nexp :: Int, mat :: QT a} deriving (Eq, Show) data (Eq a , Show a ) => QT a = C a | Q (QT a ) (QT a ) (QT a ) (QT a ) deriving (Eq, Show) cs:: (Num t) => Mat t -> [t] cs(Mat nexp (Q a b c d)) =(css (nexp-1) a c)++(css (nexp-1) b d) where css 0 (C a) (C b) = (a-b):[] css nexp (Q a b c d) (Q e f g h) = (zipWith (+) (css (nexp-1) a c) (css (nexp-1) e g))++(zipWith (+)(css (nexp-1) b d) (css (nexp-1) f h)) ``` I have this error: ``` Could not deduce (Show t) arising from a use of `Mat' from the context (Num t) bound by the type signature for cs:: Num t => Mat t -> [t] ``` I searched online and found many similar questions, but nothing seems to get close to my problem. How can I make this code work?