church.js

const assert = require("assert");

c0 = (s, z) => z;
succ = n => (s, z) => s(n(s, z));
add = (x, y) => (s, z) => x(s, y(s, z));
mul = (x, y) => (s, z) => x(z => y(s, z), z);
T = (x, y) => x;
F = (x, y) => y;
and = (a, b) => a(b, F);
or = (a, b) => a(T, b);
not = a => a(F, T);
phi = p => z => z(succ(p(T)), p(T));
pred = n => n(phi, createPair(c0, c0))(F);

createPair = (a, b) => z => z(a, b);
churchToNum = n => n(x => x + 1, 0);
churchToPair = p => [churchToNum(p(T)), churchToNum(p(F))];
churchToBool = b => b(true, false);

for (let i = 1; i < 100; i++) global["c" + i] = succ(global["c" + (i - 1)]);

assert.strictEqual(churchToNum(c15), 15);
assert.strictEqual(churchToNum(succ(c15)), 16);
assert.strictEqual(churchToNum(pred(c10)), 9);
assert.strictEqual(churchToNum(add(c15, c8)), 23);
assert.strictEqual(churchToNum(mul(c13, c2)), 26);
assert.deepEqual(churchToPair(createPair(c2, c4)), [2, 4]);
assert.strictEqual(churchToBool(T), true);
assert.strictEqual(churchToBool(F), false);
assert.strictEqual(churchToBool(not(F)), true);
assert.strictEqual(churchToBool(and(T, F)), false);
assert.strictEqual(churchToBool(or(T, F)), true);