Haskell Guard method to print the grade-CodePudding

I am new to Haskell programming, I have a requirement to print the grades based on the marks using Guard. Please find below code.

Any help would be appreciate as I am getting compiler error.

Couldn't match expected type ‘Integer -> String’
                  with actual type ‘[Char]’
    • In the expression: "MediumPass"
      In an equation for ‘printMarks’:
          printMarks mark
            | mark >= 50 && mark <= 59 = "MediumPass"
            | mark >= 60 && mark <= 69 = "High Pass"
            | mark >= 80 && mark <= 100 = "Distinction"
            | otherwise = error "invalid mark"

The code:

printMarks :: Integer -> Integer -> String

printMarks mark | mark >= 50 && mark <= 59 = "MediumPass"
                | mark >= 60 && mark <= 69 = "High Pass"
                | mark >= 80 && mark <= 100 = "Distinction"
                | otherwise = error "invalid mark" 

main = do
    putStrLn "Printing Grade"
    print(printMarks 51)

CodePudding user response：

The type of printMarks should be Integer -> String and not Integer -> Integer -> String because printMarks takes an Integer and produces a String.

printMarks :: Integer -> String

printMarks mark
    | mark >= 50, mark <= 59  = "MediumPass"
    | mark >= 60, mark <= 69  = "High Pass"
    | mark >= 80, mark <= 100 = "Distinction"
    | otherwise               = error "invalid mark" 

main = do
    putStrLn "Printing Grade"
    print(printMarks 51)

output

tarptaeya@Anmols-MBP Temp % runghc foo.hs 
Printing Grade
"MediumPass"

In Haskell f :: a -> b -> c means that if you call f with an object of type a, then it will return an function of type b -> c.