conditional-branching-with-if-when-and-cond

description: Use combinators such as if, when, and cond to branch computations based on runtime conditions, without imperative if statements. globs: "**/*.ts" alwaysApply: true

Conditional Branching with if, when, and cond

Rule: Use combinators such as if, when, and cond to branch computations based on runtime conditions, without imperative if statements.

Example

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

// Effect: Branch based on a condition
const effect = Effect.if(true, {
  onTrue: () => Effect.succeed("yes"),
  onFalse: () => Effect.succeed("no"),
}); // Effect<string>

// Option: Conditionally create an Option
const option = true ? Option.some("yes") : Option.none(); // Option<string> (Some("yes"))

// Either: Conditionally create an Either
const either = true ? Either.right("yes") : Either.left("error"); // Either<string, string> (Right("yes"))

// Stream: Conditionally emit a stream
const stream = false ? Stream.fromIterable([1, 2]) : Stream.empty; // Stream<number> (empty)

Explanation:
These combinators let you branch your computation based on a boolean or predicate, without leaving the world of composable, type-safe code.
You can also use when to run an effect only if a condition is true, or unless to run it only if a condition is false.

Explanation:
Declarative branching keeps your code composable, testable, and easy to reason about.
It also ensures that error handling and context propagation are preserved, and that your code remains consistent across different Effect types.