我推广了clojure的loop
/ recur
蹦床,以便它可以与间接递归一起使用:
const trampoline = f => (...args) => {
let acc = f(...args);
while (acc && acc.type === recur) {
let [f, ...args_] = acc.args;
acc = f(...args_);
}
return acc;
};
const recur = (...args) =>
({type: recur, args});
const even = n =>
n === 0
? true
: recur(odd, n - 1);
const odd = n =>
n === 0
? false
: recur(even, n - 1);
console.log(
trampoline(even) (1e5 + 1)); // false
但是,我必须在呼叫方明确地调用蹦床。有没有办法让它再次隐含,就像loop
/ recur
一样?
顺便说一下,这里是loop
/ recur
:
const loop = f => {
let acc = f();
while (acc && acc.type === recur)
acc = f(...acc.args);
return acc;
};
const recur = (...args) =>
({type: recur, args});
很明显,因为你想要调用trampolining,所以不能完全跳过它。最简单的事情就是将这些trampolined调用包装在你想要的API中,也许是这样的:
// Utility code
const trampoline = f => (...args) => {
let acc = f(...args);
while (acc && acc.type === recur) {
let [f, ...args_] = acc.args;
acc = f(...args_);
}
return acc;
};
const recur = (...args) =>
({type: recur, args});
// Private implementation
const _even = n =>
n === 0
? true
: recur(_odd, n - 1);
const _odd = n =>
n === 0
? false
: recur(_even, n - 1);
// Public API
const even = trampoline(_even);
const odd = trampoline(_odd);
// Demo code
console.log(
even (1e5 + 1)); // false
console.log(
odd (1e5 + 1)); // true