简单 Haskell Fibonacci 实现中的解析错误

发布于 2024-10-08 02:48:46 字数 511 浏览 5 评论 0原文

我尝试制作函数的迭代/尾递归版本来计算斐波那契数列的第 n 个数字，但出现解析错误（可能是不正确的缩进）< /代码>。为什么会发生这种情况？我正在使用的代码：

fib n
    | n < 2 = n
    | otherwise = fibhelper 0 1 2 n
    where fibhelper a b curr num
          | curr == num = a + b
          | curr < num = fibhelper b (a+b) (curr+1) num

为了清楚起见，我试图理解错误 - 为什么会发生，应该如何纠正 - 而不是试图有效地实现 fib （我理解流行的 <例如，code>zipWith 实现已经此处）。

谢谢！

原文

I've tried to make an iterative/tail-recursive version of a function to compute the nth number of the Fibonacci sequence, but I'm getting parse error (possibly incorrect indentation). Why is this happening? The code I'm using:

fib n
    | n < 2 = n
    | otherwise = fibhelper 0 1 2 n
    where fibhelper a b curr num
          | curr == num = a + b
          | curr < num = fibhelper b (a+b) (curr+1) num

To be clear, I'm trying to understand the error - why it's happening, how it should be corrected - and not trying to implement fib efficiently (I understand the popular zipWith implementation here already, for instance).

Thanks!

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趁微风不噪 2024-10-15 02:48:46

防护部分必须相对于函数名称缩进至少一个字符。因此，以下工作有效：

fib n
    | n < 2 = n
    | otherwise = fibhelper 0 1 2 n
    where fibhelper a b curr num
           | curr == num = a + b  -- moved one character to the left.
           | curr < num = fibhelper b (a+b) (curr+1) num

The guard part has to be indented at least one character relative to the function name. The following thus works:

fib n
    | n < 2 = n
    | otherwise = fibhelper 0 1 2 n
    where fibhelper a b curr num
           | curr == num = a + b  -- moved one character to the left.
           | curr < num = fibhelper b (a+b) (curr+1) num

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