The Order module provides a way to compare values and determine their order. It defines an interface Order<A> which represents a single function for comparing two values of type A. The function returns -1, 0, or 1, indicating whether the first value is less than, equal to, or greater than the second value.

Here's the basic structure of an Order:

interface Order<A> {
  (first: A, second: A): -1 | 0 | 1

Using the Built-in Orders

The Order module comes with several built-in comparators for common data types:

  • string: Used for comparing strings.
  • number: Used for comparing numbers.
  • bigint: Used for comparing big integers.
  • Date: Used for comparing Dates.

Here's how you can use these comparators:

import { Order } from "effect"
console.log(Order.string("apple", "banana")) // Output: -1, as "apple" < "banana"
console.log(Order.number(1, 1)) // Output: 0, as 1 = 1
console.log(Order.bigint(2n, 1n)) // Output: 1, as 2n > 1n

Sorting Arrays

Once you have your comparators, you can sort arrays. The ReadonlyArray module provides a handy function called sort that allows you to sort arrays without modifying the original array. Here's an example:

import { Order, ReadonlyArray } from "effect"
const strings = ["b", "a", "d", "c"]
const result = ReadonlyArray.sort(strings, Order.string)
[ 'b', 'a', 'd', 'c' ]
[ 'a', 'b', 'c', 'd' ]

You can even use an Order as a comparator in JavaScript's native Array.sort method:

import { Order } from "effect"
const strings = ["b", "a", "d", "c"]
console.log(strings) // Output: [ 'a', 'b', 'c', 'd' ]

Please note that when using Array#sort, you modify the original array. So, be cautious if you want to keep the original order. If you don't want to alter the original array, consider using ReadonlyArray.sort as shown earlier.

Deriving Orders

Sometimes, when working with more complex data structures, you may need to create custom sorting rules. The Order module allows you to do this by deriving a new Order from an existing one using the Order.mapInput function.

Imagine you have a list of Person objects, and you want to sort them by their names in ascending order. To achieve this, you can create a custom Order.

Here's how you can do it:

import { Order, ReadonlyArray } from "effect"
// Define the Person interface
interface Person {
  readonly name: string
  readonly age: number
// Create a custom sorting rule to sort Persons by their names in ascending order
const byName = Order.mapInput(Order.string, (person: Person) =>

In this example, we first import the necessary modules and define the Person interface, representing our data structure. Next, we create a custom sorting rule called byName using the mapInput function.

The mapInput function takes two arguments:

  1. The existing sorting rule you want to use as a base (Order.string in this case, for comparing strings).
  2. A function that extracts the value you want to use for sorting from your data structure ( in this case).

Once you have defined your custom sorting rule, you can apply it to sort a list of Person objects:

const persons: ReadonlyArray<Person> = [
  { name: "Charlie", age: 22 },
  { name: "Alice", age: 25 },
  { name: "Bob", age: 30 }
// Use your custom sorting rule to sort the persons array
const sortedPersons = ReadonlyArray.sort(persons, byName)
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 30 },
  { name: 'Charlie', age: 22 }

Combining Orders

The Order module not only handles basic comparisons but also empowers you to create intricate sorting rules. This is especially valuable when you need to sort data based on multiple criteria or properties.

The combine* functions in the Order module enables you to merge two or more Order instances, resulting in a new Order that incorporates the combined sorting logic. Let's walk through an example to illustrate this concept.

Imagine you have a list of people, each represented by an object with a name and an age. You want to sort this list first by name and then, for individuals with the same name, by age.

Here's how you can achieve this using the Order module:

import { Order, ReadonlyArray } from "effect"
// Define the structure of a person
interface Person {
  readonly name: string
  readonly age: number
// Create an Order to sort people by their names
const byName = Order.mapInput(Order.string, (person: Person) =>
// Create an Order to sort people by their ages
const byAge = Order.mapInput(Order.number, (person: Person) => person.age)
// Combine the two Orders to create a complex sorting logic
const byNameAge = Order.combine(byName, byAge)
const result = ReadonlyArray.sort(
    { name: "Bob", age: 20 },
    { name: "Alice", age: 18 },
    { name: "Bob", age: 18 }
  { name: 'Alice', age: 18 }, <-- by name
  { name: 'Bob', age: 18 },   <-- by age
  { name: 'Bob', age: 20 }    <-- by age

In the code above, we first create two separate Order instances: byName and byAge. These orders individually sort people by their names and ages, respectively.

Next, we use the combine function to merge these two orders into a single byNameAge order. This combined order first sorts people by name and then, for those with the same name, by age.

Finally, we apply this combined order to the array of people using ReadonlyArray.sort. The result is an array of people sorted according to the specified criteria.

Additional Useful Functions

The Order module extends its functionality by providing additional functions for common operations. These functions make it easier to work with ordered values and perform various comparisons. Let's explore each of them:

Reversing Order

The Order.reverse function does exactly what its name suggests; it reverses the order of comparison. If you have an Order that sorts values in ascending order, applying reverse will sort them in descending order.

import { Order } from "effect"
const ascendingOrder = Order.number
const descendingOrder = Order.reverse(ascendingOrder)
console.log(ascendingOrder(1, 3)) // Output: -1 (1 < 3 in ascending order)
console.log(descendingOrder(1, 3)) // Output: 1 (1 > 3 in descending order)

Comparing Values

These functions allow you to perform simple comparisons between values:

  • lessThan: Checks if one value is strictly less than another.
  • greaterThan: Checks if one value is strictly greater than another.
  • lessThanOrEqualTo: Checks if one value is less than or equal to another.
  • greaterThanOrEqualTo: Checks if one value is greater than or equal to another.
import { Order } from "effect"
console.log(Order.lessThan(Order.number)(1, 2)) // Output: true (1 < 2)
console.log(Order.greaterThan(Order.number)(5, 3)) // Output: true (5 > 3)
console.log(Order.lessThanOrEqualTo(Order.number)(2, 2)) // Output: true (2 <= 2)
console.log(Order.greaterThanOrEqualTo(Order.number)(4, 4)) // Output: true (4 >= 4)

Finding Minimum and Maximum

The min and max functions return the minimum or maximum value between two values, considering the order. These functions are particularly useful when you want to determine the smallest or largest value among multiple options.

import { Order } from "effect"
console.log(Order.min(Order.number)(3, 1)) // Output: 1 (1 is the minimum)
console.log(Order.max(Order.number)(5, 8)) // Output: 8 (8 is the maximum)

Clamping Values

The clamp function ensures that a value stays within a specified range. It takes three arguments: the value you want to clamp, the minimum bound, and the maximum bound. If the value falls outside the range, it's adjusted to the nearest bound.

import { Order } from "effect"
const clampedValue = Order.clamp(Order.number)(10, { minimum: 20, maximum: 30 })
console.log(clampedValue) // Output: 20 (10 is clamped to the nearest bound, which is 20)

Checking Value Range

The between function checks if a value falls within a specified range, inclusively. It takes three arguments: the value you want to check, the minimum bound, and the maximum bound.

import { Order } from "effect"
console.log(Order.between(Order.number)(15, { minimum: 10, maximum: 20 })) // Output: true (15 is within the range [10, 20])
console.log(Order.between(Order.number)(5, { minimum: 10, maximum: 20 })) // Output: false (5 is outside the range [10, 20])