Zipping Options in Effect-TS: A Practical Guide

In functional programming, combining multiple optional values (represented as Options) in a safe and predictable way is a common task. Effect-TS provides several methods to "zip" Options together, allowing you to combine their values or select one based on specific rules. In this article, we'll explore three key functions for zipping Options: O.zipRight, O.zipLeft, and O.zipWith.

Example 1: Returning the Second Option with O.zipRight

Concept

The O.zipRight function allows you to combine two Options, discarding the first and returning the second. This operation succeeds if both Options are Some; otherwise, it returns None.

Code

function zipping_ex01() {
  const some1 = O.some(1); // Create an Option containing the value 1
  const some2 = O.some(2); // Create an Option containing the value 2
  const none = O.none(); // Create an Option representing no value

  console.log(pipe(some1, O.zipRight(some2))); // Output: Some(2) (returns the second Option)
  console.log(pipe(some1, O.zipRight(none))); // Output: None (since the second Option is None)
  console.log(pipe(none, O.zipRight(some2))); // Output: None (since the first Option is None)
}

Explanation

• pipe(some1, O.zipRight(some2)): Both some1 and some2 are Some, so the function returns the second Option, which is Some(2).
• pipe(some1, O.zipRight(none)): Since the second Option is None, the function returns None.
• pipe(none, O.zipRight(some2)): The first Option is None, so the function returns None, regardless of the second Option.

This function is particularly useful when you want to perform an operation where the result is dependent solely on the second Option.

Example 2: Returning the First Option with O.zipLeft

Concept

The O.zipLeft function is the counterpart to O.zipRight, allowing you to combine two Options while discarding the second and returning the first. Again, this operation succeeds if both Options are Some; otherwise, it returns None.

Code

function zipping_ex02() {
  const some1 = O.some(1); // Create an Option containing the value 1
  const some2 = O.some(2); // Create an Option containing the value 2
  const none = O.none(); // Create an Option representing no value

  console.log(pipe(some1, O.zipLeft(some2))); // Output: Some(1) (returns the first Option)
  console.log(pipe(some1, O.zipLeft(none))); // Output: None (since the second Option is None)
  console.log(pipe(none, O.zipLeft(some2))); // Output: None (since the first Option is None)
}

Explanation

• pipe(some1, O.zipLeft(some2)): Since both Options are Some, the function returns the first Option, which is Some(1).
• pipe(some1, O.zipLeft(none)): The second Option is None, so the function returns None.
• pipe(none, O.zipLeft(some2)): Since the first Option is None, the function returns None.

This function is useful when the outcome should be determined by the first Option, but you still want to ensure the second Option is valid.

Example 3: Combining Options with a Function using O.zipWith

Concept

The O.zipWith function provides the most flexibility, allowing you to combine the values of two Options using a provided function. If both Options are Some, the function is applied, and the result is wrapped in a new Option. If either Option is None, the function returns None.

Code

function zipping_ex03() {
  const some1 = O.some(1); // Create an Option containing the value 1
  const some2 = O.some(2); // Create an Option containing the value 2
  const none = O.none(); // Create an Option representing no value
  const add = (a: number, b: number) => a + b;

  console.log(pipe(some1, O.zipWith(some2, add))); // Output: Some(3) (since 1 + 2 = 3)
  console.log(pipe(some1, O.zipWith(none, add))); // Output: None (since the second Option is None)
  console.log(pipe(none, O.zipWith(some2, add))); // Output: None (since the first Option is None)
}

Explanation

• pipe(some1, O.zipWith(some2, add)): Both Options are Some, so the add function is applied, resulting in Some(3).
• pipe(some1, O.zipWith(none, add)): Since the second Option is None, the function returns None.
• pipe(none, O.zipWith(some2, add)): The first Option is None, so the function returns None.

This function is ideal when you need to perform an operation on the values of two Options, as it ensures that both values are present before the operation is performed.

Conclusion

Zipping Options in Effect-TS is a powerful way to combine optional values safely. Whether you're interested in the first Option, the second, or a combination of both, the O.zipRight, O.zipLeft, and O.zipWith functions provide the tools you need to handle these scenarios efficiently. By understanding and applying these patterns, you can write more robust and predictable functional code.