Folding Options in Effect-TS: A Practical Guide

Effect-TS provides efficient ways to work with collections of Options, allowing you to perform operations on only the non-None values. One such operation is folding, where values are combined into a single result. In this article, we'll explore the O.reduceCompact function, which reduces an iterable of Options by applying a reducing function to the non-None values.

Example 1: Reducing an Iterable of Options with O.reduceCompact

Concept

The O.reduceCompact function takes an iterable of Options and reduces them to a single value by applying a reducing function to the non-None values. If an Option is None, it is ignored in the reduction.

Code

function folding_ex01() {
  const options = [O.some(1), O.none(), O.some(2), O.none(), O.some(3)]; // Create an iterable of Options
  const sum = (acc: number, value: number) => acc + value;

  console.log(pipe(options, O.reduceCompact(0, sum))); // Output: 6 (sums all non-None values: 1 + 2 + 3)
}

Explanation

• pipe(options, O.reduceCompact(0, sum)): The function starts with an initial value of 0 and iterates over the array of Options. It applies the sum function to the non-None values, accumulating the result. In this case, it adds 1, 2, and 3, resulting in 6. Any None values are ignored in the process.

This function is useful when you need to aggregate values from an iterable of Options, ensuring only the non-None values are considered.

Conclusion

Folding Options with O.reduceCompact in Effect-TS provides a powerful way to aggregate values while skipping over None values. This ensures that only meaningful values are considered in the reduction process, making it an effective tool for safely combining optional data. By leveraging this function, you can cleanly and efficiently process collections of Options without needing to handle None values explicitly in your logic.