小编Ash*_*dhi的帖子

这是取一个数字,得到它的阶乘和加倍它,但是因为基本情况如果你输入0它给2作为答案所以为了绕过它我使用了if语句,但是在输入时得到错误解析错误'如果'.真的很感激,如果你们可以帮助:)

fact :: Int -> Int
fact 0 = 1
fact n = n * fact(n-1)

doub :: Int -> Int
doub r = 2 * r

factorialDouble :: IO()
factorialDouble = do 
                    putStr "Enter a Value: "
                    x <- getLine
                    let num = (read x) :: Int
                        if (num == 0) then error "factorial of zero is 0"
                            else let y = doub (fact num) 
                                    putStrLn ("the double of factorial of " ++ x ++ " is " ++ …