当它可以在CMD上工作时，我如何运行此函数

Question

module Examples where 
import System.Random
import Data.List
cars = ["Ferrari", "Audi", "Honda","McLaren","Merc"]
cmp (x1,y1) (x2,y2) = compare y1 y2
[car | (car, n) <- sortBy cmp(zip cars (randoms (mkStdGen 123456) :: [Int]))]

我一直得到这个错误:

解析错误:模块头，导入声明或者期望的顶级声明。|7 | [car | (car, n) <- sortBy cmp(zip cars (random (mkStdGen 123456):: [Int]))]| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^:重载

有没有人对我有任何想法来修复这个，使这个函数可以运行

Answer 1

你的列表推导不是一个函数，它是一个在顶层定义的表达式，这没有多大意义。您可以定义一个输出结果的main，例如:

module Examples where 
import System.Random
import Data.List

cars :: [String]
cars = ["Ferrari", "Audi", "Honda","McLaren","Merc"]

cmp :: Ord b => (a, b) -> (a, b) -> Ordering
cmp (x1,y1) (x2,y2) = compare y1 y2
main :: IO ()   
main = print[car | (car, n) <- sortBy cmp(zip cars (randoms (mkStdGen 123456) :: [Int]))]