converting-from-nullable-option-or-either

description: Use fromNullable, fromOption, and fromEither to lift nullable values, Option, or Either into Effects or Streams for safe, typeful interop. globs: "**/*.ts" alwaysApply: true

Converting from Nullable, Option, or Either

Rule: Use fromNullable, fromOption, and fromEither to lift nullable values, Option, or Either into Effects or Streams for safe, typeful interop.

Example

import { Effect, Option, Either } from "effect";

// Option: Convert a nullable value to an Option
const nullableValue: string | null = Math.random() > 0.5 ? "hello" : null;
const option = Option.fromNullable(nullableValue); // Option<string>

// Effect: Convert an Option to an Effect that may fail
const someValue = Option.some(42);
const effectFromOption = Option.match(someValue, {
  onNone: () => Effect.fail("No value"),
  onSome: (value) => Effect.succeed(value),
}); // Effect<number, string, never>

// Effect: Convert an Either to an Effect
const either = Either.right("success");
const effectFromEither = Either.match(either, {
  onLeft: (error) => Effect.fail(error),
  onRight: (value) => Effect.succeed(value),
}); // Effect<string, never, never>

Explanation:

• Effect.fromNullable lifts a nullable value into an Effect, failing if the value is null or undefined.
• Effect.fromOption lifts an Option into an Effect, failing if the Option is none.
• Effect.fromEither lifts an Either into an Effect, failing if the Either is left.

Explanation:
Converting to Effect, Stream, Option, or Either lets you use all the combinators, error handling, and resource safety of the Effect ecosystem, while avoiding the pitfalls of null and undefined.