Λrrow is a library for Typed Functional Programming in Kotlin.

Arrow aims to provide a lingua franca of interfaces and abstractions across Kotlin libraries. For this, it includes the most popular data types such as Option, Either, Validated etc and functional operators such as traverse and computation blocks to empower users to write pure FP apps and libraries built atop higher order abstractions.

Use the list below to learn more about Λrrow's main features.

• Documentation
• Type classes: defining behaviors for data
• Effects: interfacing with external systems
• Optics: inspecting and modifying data structures

Curated external links

• Media: blogs, presentations, etc.

If you have a blog post, talk, or upcoming event on Arrow, please considering opening an issue or PR to add to the collection over at the Arrow Media repo.

Join Us

Arrow is an inclusive community powered by awesome individuals like you. As an actively growing ecosystem, Arrow and its associated libraries and toolsets are in need of new contributors! We have issues suited for all levels, from entry to advanced, and our maintainers are happy to provide 1:1 mentoring. All are welcome in Arrow.

If you’re looking to contribute, have questions, or want to keep up-to-date about what’s happening, please follow us here and say hello!

• Arrow on Twitter
• #arrow on Kotlin Slack
• #arrow-contributors on Kotlin Slack
• Arrow on Gitter

Find more details in CONTRIBUTING.

Setup

JDK

Make sure to have the latest version of JDK 1.8 (or higher) installed.

JDK 16 doesn't currently work but will do once we upgrade to Gradle 7.0

Android

Arrow supports Android starting on API 21 and up.

Gradle

Basic Setup

In your project's root build.gradle, append this repository to your list:

allprojects {
    repositories {
        mavenCentral()
    }
}

Add the dependencies into the project's build.gradle:

Λrrow Core

def arrow_version = "0.13.2"
dependencies {
    implementation "io.arrow-kt:arrow-core:$arrow_version"
}

Λrrow Core + Λrrow Optics

apply plugin: 'kotlin-kapt'

def arrow_version = "0.13.2"
dependencies {
    implementation "io.arrow-kt:arrow-optics:$arrow_version"
    kapt    "io.arrow-kt:arrow-meta:$arrow_version"
}

Λrrow Core + Λrrow Fx

def arrow_version = "0.13.2"
dependencies {
    implementation "io.arrow-kt:arrow-fx-coroutines:$arrow_version"
}

BOM file

To avoid specifying the Arrow version for every dependency, a BOM file is available:

    implementation platform("io.arrow-kt:arrow-stack:$arrow_version")

    implementation "io.arrow-kt:arrow-core"
    implementation "io.arrow-kt:arrow-fx-coroutines"
    ...

Maven

Basic Setup

Make sure to have at least the latest version of JDK 1.8 installed. Add to your pom.xml file the following properties:

<properties>
    <kotlin.version>1.4.0</kotlin.version>
    <arrow.version>0.13.2</arrow.version>
</properties>

Add the dependencies that you want to use:

<dependency>
    <groupId>io.arrow-kt</groupId>
    <artifactId>arrow-core</artifactId>
    <version>${arrow.version}</version>
</dependency>

Enabling kapt for the Optics DSL

For the Optics DSL, enable annotation processing using Kotlin plugin:

<plugin>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-maven-plugin</artifactId>
    <version>${kotlin.version}</version>
    <executions>
        <execution>
            <id>kapt</id>
            <goals>
                <goal>kapt</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>src/main/kotlin</sourceDir>
                </sourceDirs>
                <annotationProcessorPaths>
                    <annotationProcessorPath>
                        <groupId>io.arrow-kt</groupId>
                        <artifactId>arrow-meta</artifactId>
                        <version>${arrow.version}</version>
                    </annotationProcessorPath>
                </annotationProcessorPaths>
            </configuration>
        </execution>
        <execution>
            <id>compile</id>
            <phase>compile</phase>
            <goals>
                <goal>compile</goal>
            </goals>
            <configuration>
                <sourceDirs>
                    <sourceDir>src/main/kotlin</sourceDir>
                </sourceDirs>
            </configuration>
        </execution>
        <execution>
            <id>test-compile</id>
            <phase>test-compile</phase>
            <goals>
                <goal>test-compile</goal>
            </goals>
        </execution>
    </executions>
</plugin>

BOM file

To avoid specifying the Arrow version for every dependency, a BOM file is available:

  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>io.arrow-kt</groupId>
        <artifactId>arrow-stack</artifactId>
        <version>${arrow.version}</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>
  <dependencies>
    ...
  </dependencies>

Next development version

If you want to try the latest features, replace 0.13.2 with 1.0.0-SNAPSHOT and add this repository:

allprojects {
    repositories {
        ...
        maven { url "https://oss.sonatype.org/content/repositories/snapshots/" }
    }
}

License

Copyright (C) 2017 The Λrrow Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.