为什么这个Haskell程序会产生反斜杠？

问题描述

我是Haskell的新手，并编写了该程序来练习函数式编程。除了两件事，我不知道它是否是一个好的程序。

• 它有效（它向我显示了Collat​​z树中从6到1的路径）
• 它会打印太多反斜杠

next_step :: Integer -> Integer
collatz :: Integer -> String

next_step n = do
        if (n `mod` 2) == 0 then
                n `div` 2
        else
                (n * 3) + 1

collatz 1 = "1"
collatz n = (show n) ++ " -> " ++ (show (collatz (next_step n)))

main = putStrLn (collatz 6)

输出：

6 -> "3 -> \"10 -> \\\"5 -> \\\\\\\"16 -> \\\\\\\\\\\\\\\"8 -> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"4 -> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"2 -> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"1\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"\\\\\\\\\\\\\\\"\\\\\\\"\\\"\""

我希望反斜杠消失。

解决方法

collatz已经返回一个字符串，因此您无需在其上调用show：

collatz n = show(n) ++ " -> " ++ collatz (next_step n)

使用show添加引号，然后由于嵌套引号而引起反斜杠。