Skip to content

Result.md

Latest commit

 

History

History
114 lines (74 loc) · 1.74 KB

Result.md

File metadata and controls

114 lines (74 loc) · 1.74 KB
Raw

Result

Result<F, S> represents the outcome of a computation that may either succeed or fail.

  • Success<S> → successful result
  • Failure<F> → failure with an error value

It is ideal for modeling validation, parsing, IO, and API boundaries.

Motivation

Result makes failure:

  • explicit
  • typed
  • composable

Unlike exceptions, failures are values that can be inspected, transformed, and propagated safely.

Creating Results

const ok = success<number, string>("done");
const err = failure<string, number>("invalid");

Pattern Matching

res.match(
  err => console.error(err),
  val => console.log(val)
);

Both branches must be handled.

Mapping

success(10).map(x => x * 2); // Success(20)
failure("err").map(x => x); // Failure("err")

Returning a Result inside map automatically flattens.

Flattening

success(success(1)).flatten(); // Success(1)
failure(failure("e")).flatten(); // Failure("e")

Nested results are collapsed while preserving all error information.

Async Interop

promiseFlaten

await success(Promise.resolve(5)).promiseFlaten();
// Success(5)

await failure(Promise.resolve("err")).promiseFlaten();
// Failure("err")

Combining Results

ResultUtils.all

ResultUtils.all(a, b, c)(
  errs => errs,
  ([ra, rb, rc]) => ra.value + rb.value + rc.value
);

The success branch runs only if all results succeed.

Laws

  • Mapping preserves failures
  • Success identity: success(x).map(f) ≡ success(f(x))
  • Failure propagation is guaranteed

When to Use

Use Result when:

  • Failure is expected and meaningful
  • You want explicit error handling
  • Exceptions are undesirable or unsafe