✨ Backport withResolvers() from v4 to v3

lib/mod.ts

@@ -17,3 +17,4 @@ export * from "./queue.ts";
 export * from "./signal.ts";
 export * from "./ensure.ts";
 export * from "./race.ts";
+export * from "./with-resolvers.ts";

lib/with-resolvers.ts

@@ -0,0 +1,84 @@
+import { Err, Ok } from "./result.ts";
+import { action } from "./instructions.ts";
+import type { Operation, Result } from "./types.ts";
+
+/**
+ * The return type of {@link withResolvers}. It contains an operation bundled with
+ * synchronous functions that determine its outcome.
+ */
+export interface WithResolvers<T> {
+  /*
+   * An {@link Operation} that will either produce a value or raise an
+   * exception when either `resolve` or `reject` is called. No matter
+   * how many times this operation is yielded to, it will always
+   * produce the same effect.
+   */
+  operation: Operation<T>;
+
+  /**
+   * Cause {@link operation} to produce `value`. If either `resolve`
+   * or`reject` has been called before, this will have no effect.
+   *
+   * @param value - the value to produce
+   */
+  resolve(value: T): void;
+
+  /**
+   * Cause {@link operation} to raise `Error`. Any calling operation
+   * waiting on `operation` will. Yielding to `operation` subsequently
+   * will also raise the same error. * If either `resolve` or`reject`
+   * has been called before, this will have no effect.
+   *
+   * @param error - the error to raise
+   */
+  reject(error: Error): void;
+}
+
+/**
+ * Create an {link @Operation} and two functions to resolve or reject
+ * it, corresponding to the two parameters passed to the executor of
+ * the {@link action} constructor. This is the Effection equivalent of
+ * [Promise.withResolvers()]{@link
+ * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/withResolvers}
+ *
+ * @returns an operation and its resolvers.
+ */
+
+export function withResolvers<T>(): WithResolvers<T> {
+  let continuations = new Set<(result: Result<T>) => void>();
+  let result: Result<T> | undefined = undefined;
+
+  let operation: Operation<T> = action<T>(
+    (resolve, reject) => {
+      let settle = (outcome: Result<T>) => {
+        if (outcome.ok) {
+          resolve(outcome.value);
+        } else {
+          reject(outcome.error);
+        }
+      };
+
+      if (result) {
+        settle(result);
+        return () => {};
+      } else {
+        continuations.add(settle);
+        return () => continuations.delete(settle);
+      }
+    },
+  );
+
+  let settle = (outcome: Result<T>) => {
+    if (!result) {
+      result = outcome;
+    }
+    for (let continuation of continuations) {
+      continuation(result);
+    }
+  };
+
+  let resolve = (value: T) => settle(Ok(value));
+  let reject = (error: Error) => settle(Err(error));
+
+  return { operation, resolve, reject };
+}

test/abort-signal.test.ts

@@ -1,9 +1,11 @@
-import { describe, expect, it, mock } from "./suite.ts";
+import { describe, expect, it } from "./suite.ts";
 import { run, useAbortSignal } from "../mod.ts";
 
 describe("useAbortSignal()", () => {
   it("aborts whenever it passes out of scope", async () => {
-    let abort = mock.fn();
+    let state = { aborted: false };
+
+    let abort = () => state.aborted = true;
 
     let signal = await run(function* () {
       let signal = yield* useAbortSignal();
@@ -12,6 +14,6 @@ describe("useAbortSignal()", () => {
       return signal;
     });
     expect(signal.aborted).toBe(true);
-    expect(abort).toHaveBeenCalled();
+    expect(state).toEqual({ aborted: true });
   });
 });

test/main.test.ts

@@ -165,5 +165,5 @@ function* detect(
     }
     yield* sleep(10);
   }
-  expect(buffer.content).toMatch(text);
+  expect(buffer.content).toMatch(new RegExp(text));
 }

test/suite.ts

@@ -1,5 +1,5 @@
 export * from "https://deno.land/std@0.163.0/testing/bdd.ts";
-export { expect, mock } from "https://deno.land/x/expect@v0.3.0/mod.ts";
+export { expect } from "jsr:@std/expect";
 export { expectType } from "https://esm.sh/ts-expect@1.3.0?pin=v123";
 
 import {

test/with-resolvers.test.ts

@@ -0,0 +1,32 @@
+import { run, withResolvers } from "../mod.ts";
+import { describe, expect, it } from "./suite.ts";
+
+describe("withResolvers()", () => {
+  it("resolves", async () => {
+    let { operation, resolve } = withResolvers<string>();
+    resolve("hello");
+    await expect(run(() => operation)).resolves.toEqual("hello");
+  });
+  it("resolves only once", async () => {
+    let { operation, resolve, reject } = withResolvers<string>();
+    resolve("hello");
+    reject(new Error("boom!"));
+    resolve("goodbye");
+    await expect(run(() => operation)).resolves.toEqual("hello");
+  });
+  it("rejects", async () => {
+    let { operation, reject } = withResolvers<string>();
+    reject(new Error("boom!"));
+    await expect(run(() => operation)).rejects.toMatchObject({
+      message: "boom!",
+    });
+  });
+  it("rejects only once", async () => {
+    let { operation, reject } = withResolvers<string>();
+    reject(new Error("boom!"));
+    reject(new Error("bam!"));
+    await expect(run(() => operation)).rejects.toMatchObject({
+      message: "boom!",
+    });
+  });
+});

www/docs/async-rosetta-stone.mdx

@@ -8,15 +8,16 @@ know how to do it in Effection.
 The congruence between vanilla JavaScript constructs and their Effection
 counterparts is reflected in the “Async Rosetta Stone.”
 
-| Async/Await      | Effection         |
-| ---------------- | ----------------- |
-| `await`          | `yield*`          |
-| `async function` | `function*`       |
-| `Promise`        | `Operation`       |
-| `new Promise()`  | `action()`        |
-| `for await`      | `for yield* each` |
-| `AsyncIterable`  | `Stream`          |
-| `AsyncIterator`  | `Subscription`    |
+| Async/Await               | Effection         |
+| ------------------------- | ----------------- |
+| `await`                   | `yield*`          |
+| `async function`          | `function*`       |
+| `Promise`                 | `Operation`       |
+| `new Promise()`           | `action()`        |
+| `Promise.withResolvers()` | `withResolvers()` |
+| `for await`               | `for yield* each` |
+| `AsyncIterable`           | `Stream`          |
+| `AsyncIterator`           | `Subscription`    |
 
 ## `await` \<=> `yield*`
 
@@ -154,6 +155,72 @@ A key difference is that the promise body will be executing immediately, but the
 action body is only executed when the action is evaluated. Also, it is executed
 anew every time the action is evaluated.
 
+## `Promise.withResolvers()` \<=> `withResolvers()`
+
+Both `Promise` and `Operation` can be constructed ahead of time without needing to begin the process that will resolve it. To do this with
+a `Promise`, use the `Promise.withResolvers()` function:
+
+```ts
+async function main() {
+  let { promise, resolve } = Promise.withResolvers();
+
+  setTimeout(resolve, 1000);
+
+  await promise;
+
+  console.log("done!")
+}
+```
+
+In effection:
+
+```ts
+import { withResolvers } from "effection";
+
+function* main() {
+  let { operation, resolve } = withResolvers();
+
+  setTimeout(resolve, 1000);
+
+  yield* operation;
+
+  console.log("done!");
+};
+```
+
+## `Promise.withResolvers()` \<=> `withResolvers()`
+
+Both `Promise` and `Operation` can be constructed ahead of time without needing to begin the process that will resolve it. To do this with
+a `Promise`, use the `Promise.withResolvers()` function:
+
+```ts
+async function main() {
+  let { promise, resolve } = Promise.withResolvers();
+
+  setTimeout(resolve, 1000);
+
+  await promise;
+
+  console.log("done!")
+}
+```
+
+In effection:
+
+```ts
+import { withResolvers } from "effection";
+
+function* main() {
+  let { operation, resolve } = withResolvers();
+
+  setTimeout(resolve, 1000);
+
+  yield* operation;
+
+  console.log("done!");
+};
+```
+
 ## `for await` \<=> `for yield* each`
 
 Loop over an AsyncIterable with `for await`: