Haskell: function that checks if a character is a number-CodePudding

I'm trying to write a function that checks if a character is a number.

I have:

isNumber:: Int -> Bool
isNumber x = x >= 0 || x >= 0

also tried it with Guards, same problem.

isNumber2:: Int -> Bool
isNumber2 x 
    | x >= 0 = True
    | x <= 0 = True
    | otherwise = False

When I enter a number it works, it says true. If I enter a character, an error comes out because a character is not an int. So I'm wondering if you can write something else instead of Int so that you can enter numbers and characters without an error coming up.

I tried multiple different Typesignatures, but didnt work.

CodePudding user response：

If you want to know if a character is a digit, your function probably needs to accept a Char as its argument.

Now, Data.Char.ord returns the numeric code for a character.

Prelude Data.Char> ord '7'
55
Prelude Data.Char> ord '0'
48
Prelude Data.Char> ord '1'
49

You may observe that they are in order:

Prelude Data.Char> ord '7' - ord '0'
7

This math can readily turn a Char into its corresponding Int, and this should allow you to use the logic you've already shown to accomplish your goal.

CodePudding user response：

There's also a built-in function in the Data.Char module called isDigit :: Char -> Bool which checks if a character is a digit.