feat(query): add query operators

operators/query.ts

@@ -0,0 +1,36 @@
+// Copyright © 2023 Tomoki Miyauchi. All rights reserved. MIT license.
+// This module is browser compatible.
+
+import { type Err, type Ok, type Result, ResultType } from "../spec.ts";
+
+/** Returns `true` if the {@linkcode result} is a {@linkcode Ok}.
+ *
+ * @example
+ * ```ts
+ * import { isOk } from "https://deno.land/x/result_js/operators/query.ts";
+ * import { Ok, type Result } from "https://deno.land/x/result_js/spec.ts";
+ * import { assert } from "https://deno.land/std/testing/asserts.ts";
+ *
+ * const result: Result<unknown, unknown> = Ok(1);
+ * assert(isOk(result));
+ * ```
+ */
+export function isOk<T>(result: Result<T, unknown>): result is Ok<T> {
+  return result.type === ResultType.Ok;
+}
+
+/** Returns `true` if the {@linkcode result} is a {@linkcode Err}.
+ *
+ * @example
+ * ```ts
+ * import { isErr } from "https://deno.land/x/result_js/operators/query.ts";
+ * import { Err, type Result } from "https://deno.land/x/result_js/spec.ts";
+ * import { assert } from "https://deno.land/std/testing/asserts.ts";
+ *
+ * const result: Result<unknown, unknown> = Err(0);
+ * assert(isErr(result));
+ * ```
+ */
+export function isErr<E>(result: Result<unknown, E>): result is Err<E> {
+  return result.type === ResultType.Err;
+}

operators/query_test.ts

@@ -0,0 +1,25 @@
+// Copyright © 2023 Tomoki Miyauchi. All rights reserved. MIT license.
+
+import { isErr, isOk } from "./query.ts";
+import { Err, Ok } from "../spec.ts";
+import { assert, assertFalse, describe, it } from "../_dev_deps.ts";
+
+describe("isOk", () => {
+  it("should return true if it is Ok", () => {
+    assert(isOk(Ok(0)));
+  });
+
+  it("should return false if it is Err", () => {
+    assertFalse(isOk(Err(0)));
+  });
+});
+
+describe("isErr", () => {
+  it("should return true if it is Err", () => {
+    assert(isErr(Err(0)));
+  });
+
+  it("should return false if it is Ok", () => {
+    assertFalse(isErr(Ok(0)));
+  });
+});