λ dmx-fun

Explicit types for failures, absence, and validation in Java.

Get Started Developer Guide View on GitHub

dmx-fun is a Java library that makes failures, absence, and validation explicit in the type system. Instead of throwing exceptions or returning null, operations return values that encode both the happy path and the error case — composable via map and flatMap, pattern-matchable via sealed interfaces, and testable without mocks.

The core library has a single mandatory dependency: JSpecify for null-safety annotations. Everything else is optional.

Types

Eight composable types — each with a clear purpose, a consistent API, and a guide page.

Option<T> Nullability

A value that may or may not be present. The null-safe alternative.

Result<V, E> Error handling

Either a success value or a typed error. Models domain failures explicitly.

Try<V> Exception handling

Wraps a computation that may throw. Turns exceptions into values.

Validated<E, A> Validation

Like Result but accumulates multiple errors instead of failing fast.

Either<L, R> Disjoint union

A neutral disjoint union with no success/failure semantics.

Lazy<T> Deferred computation

A value computed at most once, on first access. Thread-safe memoization.

Tuple2/3/4 Product types

Typed heterogeneous tuples. Named fields without a dedicated class.

NonEmptyList<T> Collections

A list guaranteed to have at least one element at compile time.

Optional modules

Independent dependencies — add only what you need.

fun-jackson JSON

Serializers and deserializers for all dmx-fun types via Jackson.

codes.domix:fun-jackson

fun-assertj Testing

Fluent AssertJ custom assertions for all dmx-fun types.

codes.domix:fun-assertj

fun-spring Spring

Transaction support for Result, Try, and Validated. Rolls back on error without throwing exceptions.

codes.domix:fun-spring

Installation

Available on Maven Central. See the Getting Started page for full coordinates.

Gradle

implementation("codes.domix:fun:LATEST_VERSION")

Maven

<dependency>
    <groupId>codes.domix</groupId>
    <artifactId>fun</artifactId>
    <version>LATEST_VERSION</version>
</dependency>

Quick example

import dmx.fun.Option;
import dmx.fun.Try;
import java.util.function.Function;

public class QuickExample {
    record User(String name, String email, String password) {
    }

    Function<String, Option<User>> findUser = email
        -> Option.some(new User("User", email, "secret"));

    private String getUserName(String email) {
        // Handle options safely
        return findUser.apply(email)
            .map(User::name)
            .getOrElse("Anonymous");
    }

    private void parseInt(String name) {
        // Handle errors functionally
        Try.of(() -> Integer.parseInt(name))
            .recover(throwable -> {
                System.out.println("Error parsing: " + throwable.getMessage());
                return 0;
            })
            .onSuccess(System.out::println);
    }
}

Ready to dive in?

The Developer Guide covers every type in depth — design rationale, every combinator, composition patterns, and pitfalls to avoid.

Developer Guide Getting Started