Why add "Eq" type constraint without using "=="?
haskell
Solution
You need the `Eq` constraint because you're checking whether `h` is equal to `23` or `12` and whether `m` is equal to `59`. You're doing it using pattern matching, not `==`, but pattern matching against numeric literals that way still requires `Eq` (unlike pattern matching against constructors).
Problem
So, I have a very simple function that take two parameters : the first is a hour (between 0 and 23) and the second one is a minute (between 0 and 59). This function return the hour plus one minute, and format the hour in a beautiful style. By example, `hour 11 12` return `11 heures et 13 minutes`. Sorry for the french format of the hour. So, I use in this function the `show` function, and the parameters need to be a number, so I have the type declaration `(Num a, Show a) => a -> a -> String`. But, when I try the function, I got an error and GHC say to me to add the `Eq` type constraint, but I don't understand why I need the `Eq` type constraint in this case. There is the code (again, sorry for the french text used in the function, but I think that it's not very important if you don't understand the function name and the text) : ``` heure :: (Num a, Eq a, Show a) => a -> a -> String heure 23 59 = "Minuit" heure 12 m = "Midi et " ++ show (m+1) ++ " minutes" heure h 59 = show (h+1) ++ " heures" heure h m = show h ++ " heures et " ++ show (m+1) ++ " minutes" ``` So : if I don't use `Eq`, I have an error and when I use it my code is correct. Why? Thank you for your explanations!