var typed = require("typed-function");

typed.addType({
  name: 'zero',
  test: function (x) {    return x === 0;  }
});

typed.addType({
  name: 'one',
  test: function (x) {    return x === 1;  }
});

const fib = typed({
  'zero': (n) => 0,
  'one': (n) => 1,
  'any': (n) => fib(n - 1) + fib(n - 2)
});

console.log(new Array(20).fill().map((x,i) => fib(i)));