在 Effect-TS 中組合選項：實用指南

Effect-TS provides several powerful ways to combine optional values, or Options, in a functional programming context. Whether you want to pair multiple Options together or apply functions inside Options to other values, the library offers several methods to simplify these operations. In this article, we'll explore four key functions for combining Options: O.product, O.productMany, O.all, and O.ap.

Example 1: Combining Two Options into a Tuple with O.product

Concept

The O.product function allows you to combine two Options into a tuple. If both Options are Some, it returns an Option containing the tuple of both values. If either Option is None, it returns None.

Code

function combining_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(O.product(some1, some2)); // Output: Some([1, 2]) (combines both values into a tuple)
  console.log(O.product(some1, none)); // Output: None (since the second Option is None)
  console.log(O.product(none, some2)); // Output: None (since the first Option is None)
}

Explanation

• O.product(some1, some2): Both some1 and some2 are Some, so the function returns Some([1, 2]), a tuple containing both values.
• O.product(some1, none): Since the second Option is None, the function returns None.
• O.product(none, some2): Since the first Option is None, the function returns None.

This function is useful when you need to combine the values of two Options into a pair, but you still want to ensure both values exist before proceeding.

Example 2: Combining Multiple Options into a Tuple with O.productMany

Concept

The O.productMany function allows you to combine one Option with multiple Options, producing a tuple if all Options are Some. If any of the Options is None, the function returns None.

Code

function combining_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 some3 = O.some(3); // Create an Option containing the value 3
  const none = O.none(); // Create an Option representing no value

  console.log(O.productMany(some1, [some2, some3])); // Output: Some([1, 2, 3]) (combines all values into a tuple)
  console.log(O.productMany(some1, [none, some3])); // Output: None (since one of the Options is None)
}

Explanation

• O.productMany(some1, [some2, some3]): All the Options are Some, so the function returns Some([1, 2, 3]), combining all values into a tuple.
• O.productMany(some1, [none, some3]): Since one of the Options is None, the function returns None.

This function is useful when you need to combine multiple Options into a single tuple but want to ensure that all values are present before proceeding.

Example 3: Combining a Structure of Options with O.all

Concept

The O.all function combines multiple Options from an array or an object into a single Option. If all Options are Some, it returns a new Option containing the combined structure. If any Option is None, it returns None.

Code

function combining_ex03() {
  const optionsArray = [O.some(1), O.some(2), O.some(3)]; // Create an array of Options
  const optionsArrayWithNone = [O.some(1), O.none(), O.some(3)]; // Create an array of Options with a None
  const optionsObject = { a: O.some(1), b: O.some(2) }; // Create an object of Options
  const optionsObjectWithNone = { a: O.some(1), b: O.none() }; // Create an object of Options with a None

  console.log(O.all(optionsArray)); // Output: Some([1, 2, 3]) (combines all array values)
  console.log(O.all(optionsArrayWithNone)); // Output: None (since one of the array Options is None)
  console.log(O.all(optionsObject)); // Output: Some({ a: 1, b: 2 }) (combines all object values)
  console.log(O.all(optionsObjectWithNone)); // Output: None (since one of the object Options is None)
}

Explanation

• O.all(optionsArray): All the Options in the array are Some, so the function returns Some([1, 2, 3]), combining all array values.
• O.all(optionsArrayWithNone): One of the Options in the array is None, so the function returns None.
• O.all(optionsObject): All the Options in the object are Some, so the function returns Some({ a: 1, b: 2 }), combining all object values.
• O.all(optionsObjectWithNone): One of the Options in the object is None, so the function returns None.

This function is useful when dealing with multiple Options in a structure, and you want to ensure all values are present before combining them.

Example 4: Applying a Function in an Option with O.ap

Concept

The O.ap function allows you to apply a function contained in one Option to a value contained in another Option. If both Options are Some, it returns an Option containing the result of applying the function. If either Option is None, it returns None.

Code

function combining_ex04() {
  const someFn = O.some((n: number) => n * 2); // Create an Option containing a function
  const someValue = O.some(3); // Create an Option containing the value 3
  const none = O.none(); // Create an Option representing no value

  console.log(pipe(someFn, O.ap(someValue))); // Output: Some(6) (applies the function to the value)
  console.log(pipe(someFn, O.ap(none))); // Output: None (since the value Option is None)
  console.log(pipe(none, O.ap(someValue))); // Output: None (since the function Option is None)
}

Explanation

• pipe(someFn, O.ap(someValue)): Both Options are Some, so the function is applied to the value, resulting in Some(6).
• pipe(someFn, O.ap(none)): Since the value Option is None, the function returns None.
• pipe(none, O.ap(someValue)): Since the function Option is None, the result is None.

This function is useful when you need to apply a function wrapped in an Option to a value also wrapped in an Option, ensuring both exist before performing the operation.

Conclusion

Combining Options in Effect-TS allows for robust handling of optional values in a functional style. Whether you're creating tuples with O.product, combining multiple Options with O.productMany, merging structures with O.all, or applying functions with O.ap, these techniques ensure your operations are safe and predictable. By leveraging these methods, you can simplify your code while maintaining safety around missing values, making your logic more concise and reliable.

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