How to input an integer in haskell? (input in console)

Question

How can I enter an integer in the console, store it in a variable and then pass it as a parameter of a function that I have created?

So far so that it works I had to do as follows:

In the last line you can see how I have been applying the function, what I want to do is to ask for the variables by console to be applied as integers to the function and then print the result.

    mayor :: Int -> Int -> Double
    mayor x y =
        if  x < y 
        then 0.1
            else 0.3


    compra :: Int -> Int -> Int -> Int -> Int -> Int -> Double
    compra n v u iva p vp =
        let valor_compra = (fromIntegral v) * (fromIntegral n) * (1 - mayor n u)
            valor_iva = valor_compra * (fromIntegral iva) / 100
            valor_puntos = fromIntegral (p * vp)
            efectivo = if (valor_puntos < valor_compra) then valor_compra-valor_puntos else 0
        in  valor_iva + efectivo

    main = do
    print (compra 20 2000 7 14 10 1500)

The way I do it gives me as a result 16920.0

Solution 1

Use getLine or readLn and then parse the input value to the type you need it to be like so :

mayor :: Int -> Int -> Double
mayor x y =
    if  x < y 
    then 0.1
        else 0.3


compra :: Int -> Int -> Int -> Int -> Int -> Int -> Double
compra n v u iva p vp =
    let valor_compra = (fromIntegral v) * (fromIntegral n) * (1 - mayor n u)
        valor_iva = valor_compra * (fromIntegral iva) / 100
        valor_puntos = fromIntegral (p * vp)
        efectivo = if (valor_puntos < valor_compra) then valor_compra-valor_puntos else 0
    in  valor_iva + efectivo

main = do
       putStrLn "enter value for x: "
       input1 <- getLine
       putStrLn "enter value for y: " 
       input2 <- getLine 
       let x = (read input1 :: Int)
       let y = (read input2 :: Int)
       print (compra x y 7 14 10 1500)

Solution 2

If the integers are entered on same line, we can do something like below. The below program reads two numbers separated by space and prints their sum.

main :: IO()
main = do
    line <- getLine
    let a = (read (takeWhile (/= ' ') line) :: Int)
    let b = (read (drop 1 (dropWhile (/= ' ') line)) :: Int)
    putStrLn (show (a+b)) 

Comments

[delta1020]

Thank you very much, it served me perfect