c - 在 C 中实现 F# List.scan？

Question

您将如何实现与 List.scan 具有相同行为的函数在 F# 中？

这是描述:

Applies a function to each element of the collection, threading an accumulator argument through the computation. This function takes the second argument, and applies the function to it and the first element of the list. Then, it passes this result into the function along with the second element, and so on. Finally, it returns the list of intermediate results and the final result. (link)

当然，我已经尝试过自己，这是我的伪代码(顺便说一句，我不希望您提供有效的 c 代码): 对于电话 scan(myop, ne, x) ，我有伪代码

int n = length(x);
char *b = (char*)malloc(n); //Allocate n bytes
b[0] = ne;
int i = 0;
while (i < n) {
    bool tmp = myop(b[i-1], x[i]);
    bool b[i] = tmp;
    i = i+1;
}
bool list y = b;

但这对 i > 0 失败了从此 b[i]未初始化。你将如何实现这一点？

Answer 1

but this fails for i > 0 since then b[i] is not initialized

在你的伪代码中:

bool tmp = myop(b[i-1], x[i]);

i = 0时会失败(意思是第一次进入while循环)，因为你尝试访问索引 -1 ( i = 0 ，所以 b[i-1] 变成 b[-1] ) 的 b ，这是未定义的行为。

你必须开始 while在 i = 1 处循环至少。所以，在循环之前:

b[0] = ne;
int i = 0;

可以改为:

b[0] = ne;
// do something with b[0] if you want.
int i = 1;