closure.js

import test from 'ava';

import {closure, enumerate, list, takewhile} from '../../../src/index.js';

// https://oeis.org/A006577
const Collatz = (x) => (x % 2 === 1 ? 3 * x + 1 : Math.floor(x / 2));

const A006577 = [
	0,
	1,
	7,
	2,
	5,
	8,
	16,
	3,
	19,
	6,
	14,
	9,
	9,
	17,
	17,
	4,
	12,
	20,
	20,
	7,
	7,
	15,
	15,
	10,
	23,
	10,
	111,
	18,
	18,
	18,
	106,
	5,
	26,
	13,
	13,
	21,
	21,
	21,
	34,
	8,
	109,
	8,
	29,
	16,
	16,
	16,
	104,
	11,
	24,
	24,
	24,
	11,
	11,
	112,
	112,
	19,
	32,
	19,
	32,
	19,
	19,
	107,
	107,
	6,
	27,
	27,
	27,
	14,
	14,
	14,
	102,
	22,
];

function macro(t, n, a) {
	const sequence = list(takewhile((x) => x !== 1, closure(Collatz, n)));

	t.is(sequence.length, a);
}

macro.title = (_, n, a) => `closure [A006577] > a(${n}) = ${a}`;

for (const [n, a] of enumerate(A006577, 1)) {
	test(macro, n, a);
}