accumulate-multiple-errors-with-either

description: Use Either to model computations that may fail, making errors explicit and type-safe. globs: "**/*.ts" alwaysApply: true

Accumulate Multiple Errors with Either

Rule: Use Either to model computations that may fail, making errors explicit and type-safe.

Example

import { Either } from "effect";

// Create a Right (success) or Left (failure)
const success = Either.right(42); // Either<never, number>
const failure = Either.left("Something went wrong"); // Either<string, never>

// Pattern match on Either
const result = success.pipe(
  Either.match({
    onLeft: (err) => `Error: ${err}`,
    onRight: (value) => `Value: ${value}`,
  })
); // string

// Combine multiple Eithers and accumulate errors
const e1 = Either.right(1);
const e2 = Either.left("fail1");
const e3 = Either.left("fail2");

const all = [e1, e2, e3].filter(Either.isRight).map(Either.getRight); // [1]
const errors = [e1, e2, e3].filter(Either.isLeft).map(Either.getLeft); // ["fail1", "fail2"]

Explanation:

• Either.right(value) represents success.
• Either.left(error) represents failure.
• Pattern matching ensures all cases are handled.
• You can accumulate errors or results from multiple Eithers.

Explanation:
Either is a foundational data type for error handling in functional programming.
It allows you to accumulate errors, model domain-specific failures, and avoid exceptions and unchecked errors.