Schniz · July 15, 2025 06:31 · Jul 15, 2025
diff --git a/cancelable.ts b/cancelable.ts
@@ -0,0 +1,47 @@
+/**
+ * Something that can be yielded
+ */
+interface Yieldable<T> {
+  (signal: AbortSignal): Promise<T>;
+}
+
+/**
+ * Executes a generator function that yields promises, allowing for cancellation via an AbortSignal.
+ */
+export async function co<B, C>(
+  signal: AbortSignal,
+  fn: () => Generator<Yieldable<any>, B, C>
+): Promise<B> {
+  const gen = fn();
+  let current = gen.next();
+  while (!signal.aborted && !current.done) {
+    const v = await current.value(signal);
+    if (signal.aborted) {
+      current = gen.throw(signal.reason);
+    } else {
+      current = gen.next(v);
+    }
+  }
+
+  signal.throwIfAborted();
+  if (!current.done) {
+    throw new UnfinishedGeneratorError();
+  }
+
+  return current.value;
+}
+
+class UnfinishedGeneratorError extends Error {
+  name = 'UnfinishedGeneratorError';
+  constructor() {
+    super('unfinished generator');
+  }
+}
+
+export function* cancelable<T>(fn: Yieldable<T>): Generator<typeof fn, T, T> {
+  return yield fn;
+}
+
+export function* from<T>(promise: Promise<T>) {
+  return yield* cancelable(() => promise);
+}