haskell - 如何在haskell中输入整数？ (在控制台输入)

Question

如何在控制台中输入一个整数，将其存储在变量中，然后将其作为我创建的函数的参数传递？

到目前为止，为了使其有效，我必须执行以下操作:

在最后一行中，您可以看到我如何应用该函数，我想要做的是通过控制台请求变量作为整数应用于函数，然后打印结果。

    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)

我这样做的方式给了我结果16920.0

Answer 1

使用getLine或readLn，然后将输入值解析为您需要的类型，如下所示:

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)