为什么这个 Haskell 程序会产生反斜杠？

Question

我是 Haskell 的新手，写这个程序是为了练习函数式编程。我不知道它是否是一个好程序，除了两件事。

• 它有效（它向我展示了 Collat​​z 树中从 6 到 1 的路径）
• 它打印了太多的反斜杠

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。

Answer 1

collatz 已经返回一个字符串，所以你不需要在它上面调用show：

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

使用show 添加引号，然后由于嵌套引号导致反斜杠。