Either Kotlin Library

A Kotlin library providing a functional Either type for handling computations that can succeed or fail. Inspired by functional programming paradigms, this library allows safe and expressive error handling and transformation of values.

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Overview

The Either type represents a value of one of two possible types:

• Success – indicates a successful computation or state.
• Failure – indicates a failure computation or state.

This library provides utility functions for:

• Mapping and transforming values.
• Binding (monadic operations).
• Traversing and collecting multiple Either values.
• Recovering from failures.
• Swapping and querying Either states.

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Features

Creating Either Values

val success: Either<Nothing, Int> = success(42)
val failure: Either<Int, Nothing> = failure(1)

Accessors

val value = success.orNull()          // 42
val failed = failure.failureOrNull()  // 1
val isSuccess = success.isSuccess     // true
val isFailure = failure.isFailure     // true

Mapping Values

val mapped = success.map { it + 1 }       // success(43)
val failedMapped = failure.mapFailure { it + 1 } // failure(2)

Binding (FlatMapping)

val result = success.bind { success(it + 1) }  // success(43)
val failResult = failure.bindFailure { success("Recovered") } // success("Recovered")

Recovering from Failures

val recovered = failure.recover { it * 2 } // success(2)

Swapping

val swapped = success.swap()  // failure(42)
val swappedFail = failure.swap() // success(1)

Either Operations

val value = success.either(
    onSuccess = { it },
    onFailure = { -1 }
) // 42

Traversing Collections

Supports List, Iterable, Sequence, and Iterator:

val list = listOf(1, 2, 3)
val traversed = list.traverseApplicative { success(it + 1) } // success(listOf(2, 3, 4))

• applicative() – traverses all successes or all failures.
• monadic() – stops at the first failure.

Collecting Multiple Eithers

val eithers = listOf(success(1), failure(2))
val collected = eithers.collectApplicative() // failure(listOf(2))

• applicative() – collects all successes or all failures.
• monadic() – stops at the first failure.

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Usage

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License

MIT License © 2025