https://github.com/alexandrepiveteau/functional-kotlin
Functional Programming goodies for Kotlin
https://github.com/alexandrepiveteau/functional-kotlin
composition functional-programming kotlin monads
Last synced: about 1 month ago
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Functional Programming goodies for Kotlin
- Host: GitHub
- URL: https://github.com/alexandrepiveteau/functional-kotlin
- Owner: alexandrepiveteau
- License: mit
- Created: 2018-09-02T15:58:38.000Z (about 7 years ago)
- Default Branch: master
- Last Pushed: 2018-10-03T07:28:02.000Z (about 7 years ago)
- Last Synced: 2025-09-07T07:32:42.026Z (about 1 month ago)
- Topics: composition, functional-programming, kotlin, monads
- Language: Kotlin
- Homepage:
- Size: 150 KB
- Stars: 9
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE.md
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README
# functional-kotlin
[](https://jitpack.io/#alexandrepiveteau/functional-kotlin)
This repository contains some utilies for functional programming in the Kotlin programming language.
The OSS license can be found in the [LICENSE.md](LICENSE.md) file of the repository.
## Installation
This library is available on [JitPack.io](https://jitpack.io/#alexandrepiveteau/functional-kotlin). Make
sure to add the following Maven repository in your root **build.gradle** file :
```
allprojects {
repositories {
...
maven { url 'https://jitpack.io' }
}
}
```
You can now add the library modules in your application **build.gradle** file :
```
dependencies {
implementation "com.github.alexandrepiveteau.functional-kotlin:functional-collections:0.3.0"
implementation "com.github.alexandrepiveteau.functional-kotlin:functional-composition:0.3.0"
implementation "com.github.alexandrepiveteau.functional-kotlin:functional-monads:0.3.0"
implementation "com.github.alexandrepiveteau.functional-kotlin:functional-monads-probabilistic:0.3.0"
}
```
## Usage
The library contains the following modules :
- **functional-collections** - Offers some utilities for working with collections in a functional manner.
- **functional-composition** - Offers some infix operators for function composition.
- **functional-monads** - Offers some implementations for the `Maybe`, `Either` and `Reader` monads.
- **functional-probabilistic** - Offers some **extremely experimental** implementations for the `Distribution` monads. The package name will be changed once the API is considered more stable.
### functional-composition
The library offers the `compose`, `andThen` and `forwardCompose` operators, as well as a handy `..` syntax for function composition.
The functions `compose` and `..` have the same effect. The functions `andThen` and `forwardCompose` have the same effect as well, and
do composition in the opposite direction as `compose`/`..`.
The infix operators are quite straightforward to use :
```kotlin
val generateNumber : () -> Int = { 42 }
val doubleNumber: (Int) -> Int = { it * 2 }
val generateDoubleNumber = generateNumber forwardCompose doubleNumber
println(generateDoubleNumber()) // Prints "84".
```
### functional-monads
#### Maybe
Let's start with the `Maybe` monad :
```kotlin
data class Capital(val country: String, val name: String)
val response: Maybe> = emptyMaybe() // For example, might be a web API callback.
val message = response.map { it.singleOrNull { it.country == "Switzerland" } }
.flatMap { it.toMaybe() }
.fold({ (_, name) -> "Found the capital of Switzerland : $name." },
{ "No capital found for Switzerland." })
println(message) // Prints "No capital found for Switzerland."
```
As you can see in the previous example, multiple operators are provided for the `Maybe` type. The functions `map`
and `flatMap` are present, as well as a `fold`function to accumulate the result of the `Maybe`. You'll also notice
that a convenience `toMaybe()` extension function can be used to transform any instance to a `Maybe`.
You can always create some `Maybe` by using the `maybeOf(...)` and `emtpyMaybe()` functions.