a fixed-point combinator in JavaScript

fixedpoint.js

// Z = \t. (\f. t (\z. f f z)) (\f. t (\z. f f z))
function Z(t) {
  return ( (f) => t((z) => (f(f))(z)) ) ( (f) => t((z) => (f(f))(z)) );
}

function fact_template(f) {
  return function(n) {
    if (n <= 1) {
      return 1;
    } else {
      return n * f(n - 1);
    }
  }
}

var fact = Z(fact_template);

console.log(fact(3));
console.log(fact(5));