Lykn

genfn: Anonymous Generators

genfn is to genfunc what fn is to func — an anonymous generator with positional typed parameters.

;; Zero-arg generator
(bind gen (genfn () (yield 1) (yield 2) (yield 3)))

(for-of n (gen)
  (console:log n))     ;; 1, 2, 3

const gen = function*() {
  yield 1;
  yield 2;
  yield 3;
};
for (const n of gen()) {
  console.log(n);
}

With Typed Parameters

(bind range (genfn (:number start :number end)
  (for (let i start) (< i end) (+= i 1)
    (yield i))))

(for-of n (range 0 5)
  (console:log n))

const range = function*(start, end) {
  if (typeof start !== "number" || Number.isNaN(start))
    throw new TypeError(
      "anonymous: arg 'start' expected number, got " + typeof start);
  if (typeof end !== "number" || Number.isNaN(end))
    throw new TypeError(
      "anonymous: arg 'end' expected number, got " + typeof end);
  for (let i = start; i < end; i += 1) {
    yield i;
  }
};

With :yields

(bind doubler (genfn (:number x) :yields :number
  (yield (* x 2))
  (yield (* x 3))))

(for-of n (doubler 5)
  (console:log n))     ;; 10, 15

Per-yield type checks work the same as in genfunc — the yielded value is validated before being produced.

When to Use genfn

genfn is useful when passing a generator as a value — to a higher-order function, as an argument, or stored in a data structure. For most named generators, prefer genfunc — the name appears in stack traces and error messages.