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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, type classes and abstractions such as Option, Try, Either, IO, Functor, Applicative, Monad 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.

  • Patterns: tutorials and approaches to day-to-day challenges using FP
  • Libraries: all the libraries provided by Λrrow
  • Type classes: defining behaviors for data
  • Data types: common abstractions
  • Effects: interfacing with external systems
  • Optics: inspecting and modifying data structures

Gradle

Basic Setup

Make sure to have the latest version of JDK 1.8 installed.

In your project’s root build.gradle append these repositories to your list.

allprojects {
    repositories {
        mavenCentral()
        jcenter()
        maven { url "https://dl.bintray.com/arrow-kt/arrow-kt/" } 
        maven { url 'https://oss.jfrog.org/artifactory/oss-snapshot-local/' } // for SNAPSHOT builds
    }
}

Next development version 0.10.1

Add the dependencies into the project’s build.gradle

Λrrow Core

def arrow_version = "0.10.1-SNAPSHOT"
dependencies {
    compile "io.arrow-kt:arrow-core:$arrow_version"
    compile "io.arrow-kt:arrow-syntax:$arrow_version"
    kapt    "io.arrow-kt:arrow-meta:$arrow_version"
}

Λrrow Core + Λrrow Optics

def arrow_version = "0.10.1-SNAPSHOT"
dependencies {
    compile "io.arrow-kt:arrow-optics:$arrow_version"
    compile "io.arrow-kt:arrow-syntax:$arrow_version"
    kapt    "io.arrow-kt:arrow-meta:$arrow_version"
}

Λrrow Core + Λrrow Fx

def arrow_version = "0.10.1-SNAPSHOT"
dependencies {
    compile "io.arrow-kt:arrow-fx:$arrow_version"
    compile "io.arrow-kt:arrow-syntax:$arrow_version"
    kapt    "io.arrow-kt:arrow-meta:$arrow_version"
}

Λrrow Core + Λrrow Optics + Λrrow Fx

def arrow_version = "0.10.1-SNAPSHOT"
dependencies {
    compile "io.arrow-kt:arrow-fx:$arrow_version"
    compile "io.arrow-kt:arrow-optics:$arrow_version"
    compile "io.arrow-kt:arrow-syntax:$arrow_version"
    kapt    "io.arrow-kt:arrow-meta:$arrow_version"
}

Here is the complete library list for a more granular dependency set-up.

Additional Setup

For projects that wish to use their own @higherkind, @optics and other meta programming facilities provided by Λrrow the setup below is also required:

Add the dependencies into the project’s build.gradle

apply plugin: 'kotlin-kapt' //optional
apply from: rootProject.file('gradle/generated-kotlin-sources.gradle') //only for Android projects

def arrow_version = "0.10.1-SNAPSHOT"
dependencies {
    ...
    kapt    'io.arrow-kt:arrow-meta:$arrow_version' //optional
    ...
}

gradle/generated-kotlin-sources.gradle

apply plugin: 'idea'

idea {
    module {
        sourceDirs += files(
                'build/generated/source/kapt/main',
                'build/generated/source/kapt/debug',
                'build/generated/source/kapt/release',
                'build/generated/source/kaptKotlin/main',
                'build/generated/source/kaptKotlin/debug',
                'build/generated/source/kaptKotlin/release',
                'build/tmp/kapt/main/kotlinGenerated')
        generatedSourceDirs += files(
                'build/generated/source/kapt/main',
                'build/generated/source/kapt/debug',
                'build/generated/source/kapt/release',
                'build/generated/source/kaptKotlin/main',
                'build/generated/source/kaptKotlin/debug',
                'build/generated/source/kaptKotlin/release',
                'build/tmp/kapt/main/kotlinGenerated')
    }
}

Linting

Some linters might complaint about some code practices that are common when working with functional programming. You can read more about how to solve this problem in the Linting section.

Maven

Basic Setup

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

<properties>
    <kotlin.version>1.3.0</kotlin.version>
     <arrow.version>0.9.0</arrow.version>
</properties>

Add the dependencies that you want to use

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

Enabling kapt

Enable annotaton 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>