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const assert = require('assert'); | |
const cons = (a, list) => _cons => _cons(a, list); | |
const car = list => list(head => head); | |
const cdr = list => list((_, tail) => tail); | |
const nil = () => null; | |
const is_nil = list => car(list) === nil(); | |
const length = list => | |
is_nil(list) ? 0 : 1 + length(cdr(list)); | |
const nth = (list, n) => | |
(n == 0) ? car(list) : nth(cdr(list), n - 1); | |
const foldl = (f, list, acc) => | |
is_nil(list) ? acc : foldl(f, cdr(list), f(acc, car(list))); | |
const foldr = (f, list, acc) => | |
is_nil(list) ? acc : f(foldr(f, cdr(list), acc), car(list)); | |
const reverse = list => | |
foldl((acc, x) => cons(x, acc), list, nil); | |
const map = (f, list) => | |
foldr((acc, x) => cons(f(x), acc), list, nil); | |
const filter = (f, list) => | |
is_nil(list) ? nil : ( | |
f(car(list)) | |
? cons(car(list), filter(f, cdr(list))) | |
: filter(f, cdr(list))); | |
const L = cons(1, cons(2, cons(3, cons(4, cons(5, nil))))); | |
assert( length(L) === 5 ); | |
assert( nth(L, 3) === 4 ); | |
assert( car(L) === 1 ); | |
assert( car(cdr(L)) === 2 ); | |
assert( car(map(a => a * 2, L)) === 2 ); | |
assert( car(filter(a => a > 3, L)) === 4 ); | |
assert( car(reverse(L)) === 5 ); |
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