lambda-calculus-with-js/examples/number.test.js

Using JS' anonymous functions to perform lambda calculus

import t from 'tape';
import { test } from '..';
import { getLambdaEq } from '../test';
import { getBool } from './bool';
import { deNumber, eq, factorial, ge, getNumber, gt, isZero, le, ls, minus, multi, ne, plus, pred, succ, } from './number';
const n1 = getNumber(1);
const n2 = getNumber(2);
const n8 = getNumber(8);
t('number', t => {
    const eqL = getLambdaEq(t);
    t.deepEqual(test(n1), test(f => x => f(x)));
    t.deepEqual(test(n2), test(f => x => f(f(x))));
    t.deepEqual(test(n8), test(f => x => f(f(f(f(f(f(f(f(x))))))))));
    function fact(n) {
        return n === 0 ? 1 : n * fact(n - 1);
    }
    const sigTs = [
        [isZero, n => getBool(n === 0), '0 =='],
        [succ, n => getNumber(n + 1), '1 +'],
        [pred, n => getNumber(n ? n - 1 : 0), '-1 +'],
        [factorial, n => getNumber(fact(n)), 'fact'],
    ];
    const binTs = [
        [plus, (a, b) => getNumber(a + b), '+'],
        [multi, (a, b) => getNumber(a * b), '*'],
        [minus, (a, b) => getNumber(a - b < 0 ? 0 : a - b), '-'],
        [le, (a, b) => getBool(a <= b), '<='],
        [gt, (a, b) => getBool(a > b), '>'],
        [ge, (a, b) => getBool(a >= b), '>='],
        [ls, (a, b) => getBool(a < b), '<'],
        [eq, (a, b) => getBool(a === b), '=='],
        [ne, (a, b) => getBool(a !== b), '!='],
    ];
    const l = Array(10).fill(0)
        .map((_, b) => b);
    for (const a of l) {
        t.equal(deNumber(getNumber(a)), a);
        for (const [fn, cm, msg] of sigTs) {
            if (a > 6 && fn === factorial)
                continue;
            eqL(fn(getNumber(a)), cm(a), `${msg} ${a}`);
        }
        for (const b of l) {
            for (const [fn, cm, msg] of binTs) {
                eqL(fn(getNumber(a))(getNumber(b)), cm(a, b), `${a} ${msg} ${b}`);
            }
        }
    }
    t.end();
});