5 javascript recursion functional-programming tail-recursion
我正在试验功能List类型和结构共享。由于 Javascript 没有尾递归模约束优化,我们不能List像这样编写组合器,因为它们不是堆栈安全的:
const list =
[1, [2, [3, [4, [5, []]]]]];
const take = n => ([head, tail]) =>
n === 0 ? []
: head === undefined ? []
: [head, take(n - 1) (tail)];
console.log(
take(3) (list) // [1, [2, [3, []]]]
);Run Code Online (Sandbox Code Playgroud)
现在我尝试take递归地实现尾部,以便我可以依赖 TCO(Promise在 Ecmascript 中仍然未解决)或使用蹦床(在示例中省略以保持简单):
const list =
[1, [2, [3, [4, [5, []]]]]];
const safeTake = n => list => {
const aux = (n, acc, [head, tail]) => n === 0 ? acc
: head === undefined ? acc
: aux(n - 1, [head, acc], tail);
return aux(n, [], list);
};
console.log(
safeTake(3) (list) // [3, [2, [1, []]]]
);Run Code Online (Sandbox Code Playgroud)
这有效,但新创建的列表顺序相反。我怎样才能以纯功能的方式解决这个问题?