Lifting Functions into the Option Context in Effect-TS: A Practical Guide

In functional programming, lifting refers to the process of adapting a function to work within a specific context, such as an Option. Effect-TS provides convenient methods to lift functions into the Option context, allowing you to apply functions or predicates to Option values seamlessly. In this article, we'll explore two key functions for lifting: O.lift2 and O.liftPredicate.

Example 1: Lifting a Binary Function with O.lift2

Concept

The O.lift2 function allows you to lift a binary function (a function that takes two arguments) into the Option context. This enables you to apply the function to two Option values. If both Options are Some, the function is applied; if either Option is None, the result is None.

Code

function lifting_ex01() {
  const add = (a: number, b: number) => a + b;
  const liftedAdd = O.lift2(add);

  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, liftedAdd(some2))); // Output: Some(3) (1 + 2 = 3)
  console.log(pipe(some1, liftedAdd(none))); // Output: None (since one Option is None)
  console.log(pipe(none, liftedAdd(some2))); // Output: None (since one Option is None)
}

Explanation

• pipe(some1, liftedAdd(some2)): Both Options are Some, so the add function is applied to the values, resulting in Some(3) (1 + 2 = 3).
• pipe(some1, liftedAdd(none)): Since one of the Options is None, the result is None.
• pipe(none, liftedAdd(some2)): Again, since one of the Options is None, the result is None.

This function is particularly useful when you want to apply a binary function to two Option values while handling the cases where one or both Options might be None.

Example 2: Lifting a Predicate Function with O.liftPredicate

Concept

The O.liftPredicate function allows you to lift a predicate (a function that returns a boolean) into the Option context. This converts the predicate into a function that returns an Option. If the predicate is satisfied, it returns Some with the value; otherwise, it returns None.

Code

function lifting_ex02() {
  const isPositive = (n: number) => n > 0;
  const liftedIsPositive = O.liftPredicate(isPositive);

  console.log(liftedIsPositive(1)); // Output: Some(1) (1 is positive)
  console.log(liftedIsPositive(-1)); // Output: None (-1 is not positive)
  console.log(liftedIsPositive(0)); // Output: None (0 is not positive)
}

Explanation

• liftedIsPositive(1): The predicate isPositive is satisfied (1 > 0), so the result is Some(1).
• liftedIsPositive(-1): The predicate is not satisfied (-1 is not greater than 0), so the result is None.
• liftedIsPositive(0): The predicate is not satisfied (0 is not greater than 0), so the result is None.

This function is useful when you want to apply a predicate to a value and lift the result into the Option context, returning Some when the condition is met and None otherwise.

Conclusion

Lifting functions into the Option context in Effect-TS allows you to work seamlessly with optional values while applying functions or predicates. With O.lift2, you can apply binary functions to Options, ensuring that operations are only performed when both values are present. Similarly, O.liftPredicate enables you to convert predicates into functions that return an Option, making it easy to encapsulate conditions within the Option context. By using these tools, you can simplify your code and manage optional values more effectively in functional programming.

Comments

[Zuhalcode]

How to make the code block coloured ?

[Alessandro Maclaine]

@zuhalcode put the language after the three ticks, '''typescript, but use back ticks