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| const If = p => a => b => p(a)(b) | |
| const True = a => b => a | |
| const False = a => b => b | |
| const One = s => z => s(z); | |
| const Two = s => z => s(s(z)); | |
| const Three = s => z => s(s(s(z))); | |
| const Succ = n => f => x => f(n(f)(x)) | |
| const Plus = m => n => f => x => m(f)(n(f)(x)) | |
| // z combinator | |
| const z = f => (x => f(v => x(x)(v)))(x => f(v => x(x)(v))) | |
| const Pair = x => y => z => z(x)(y) | |
| const First = p => p(x => y => x) | |
| const Second = p => p(x => y => y) | |
| // List | |
| const Cons = Pair | |
| const Head = First | |
| const Tail = Second | |
| const Nil = False | |
| const isNil = l => l(h => t => d => False)(True) | |
| const Map = z(map => list => f => { | |
| // 由于 js 立即求值会爆栈, 这里包装一下 | |
| return If(isNil(list))((/* thunk */) => Nil)( | |
| (/* thunk */) => Cons(f(Head(list)))(map(Tail(list))(f)(/* Map 返回的实际上是个 thunk, 这里手动调用一次 */)) | |
| ) | |
| }) | |
| // [1, 2, 3] | |
| const input = Cons(One)(Cons(Two)(Cons(Three)(Nil))) | |
| const AddOne = x => Plus(x)(One) | |
| // [2, 3, 4] | |
| const result = Map(input)(AddOne)(/* Map 返回的实际上是个 thunk, 这里手动调用一次 */) | |
| console.log('Input:', convertNumList(input)) | |
| console.log('Result:', convertNumList(result)) | |
| // Helpers | |
| function convertNumList(listNode) { | |
| let current = listNode | |
| const res = [] | |
| while (isNil(current)(false)(true)) { | |
| res.push(convert(Head(current))) | |
| current = Tail(current) | |
| } | |
| return res | |
| } | |
| function s(n) { | |
| return n + 1 | |
| } | |
| function convert(f) { | |
| return f(s)(0) | |
| } |
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