Functional Reactive Lib

Error handling with Result

Fri, 15 May 2026 00:00:00 +0000

The problem

You have a pipeline that parses a config value, looks up a record by id, and renders a label. Each step can fail — and the classic Java solution is a try/catch ladder or Optional.flatMap chains that silently swallow the reason for failure.

The Result way

Result<String> label = Result.ofNullable(System.getProperty("user.id"))
 .map(Integer::parseInt)
 .flatMap(repo::findById)
 .map(User::displayName);

label.ifPresentOrElse(
 System.out::println,
 err -> log.warn("could not render label: {}", err)
);

No exceptions escape, every failure carries a reason, and the happy path reads top-to-bottom.

Getting Started

Mon, 01 Jan 0001 00:00:00 +0000

Add the dependency

Maven:

<dependency>
 <groupId>com.svenruppert</groupId>
 <artifactId>functional-reactive</artifactId>
 <version>06.01.01</version>
</dependency>

Gradle (Kotlin DSL):

implementation("com.svenruppert:functional-reactive:06.01.01")

Your first `Result`

import com.svenruppert.functional.model.Result;

Result<Integer> parsed = Result.ofNullable(System.getProperty("port"))
 .map(Integer::parseInt);

parsed.ifPresentOrElse(
 port -> System.out.println("Port = " + port),
 error -> System.err.println("No port: " + error)
);

Next steps

Read the Result<T> reference
Learn how to chain async work with the CompletableFutureQueue
Browse Tutorials for end-to-end examples

Result

Mon, 01 Jan 0001 00:00:00 +0000

Result<T> is the central error-handling primitive of functional-reactive. Think of it as Optional<T> with a reason for the absence.

Result<User> user = repository.findById(id);

user.ifPresentOrElse(
 u -> log.info("Found {}", u),
 err -> log.warn("Lookup failed: {}", err)
);

Construction

Method	Description
`Result.success(t)`	Wraps a non-null value.
`Result.failure(reason)`	Marks the absence of a value with a message.
`Result.ofNullable(t)`	Success if non-null, otherwise failure.
`Result.fromOptional(opt)`	Bridge from `java.util.Optional`.

Transformations

map(Function) — transform the value if present.
flatMap(Function<T, Result<U>>) — chain another Result-returning operation.
or(Supplier) — fall back to another Result.

Combinators

thenCombine(value, BiFunction) — combine with a plain value.
thenCombineAsync(value, BiFunction) — same, but asynchronous.

Terminal operations

ifPresent(Consumer) / ifAbsent(Runnable) / ifFailed(Consumer<String>)
ifPresentOrElse(Consumer, Consumer<String>)
stream() — zero-or-one element stream.
toOptional() — back to java.util.Optional.

When to reach for Result

Use Result whenever absence has a reason the caller cares about — failed parsing, missing config, lookups that may fail. Reach for Optional when absence is the entire information.

Async pipelines with CompletableFutureQueue

Fri, 15 May 2026 00:00:00 +0000

Coming soon.

Tuples (Pair…Sept)

Mon, 01 Jan 0001 00:00:00 +0000

The model package provides immutable, generic tuples from Single<T> up to Sept<T1…T7>, each with proper equals, hashCode and toString.

Pair<String, Integer> entry = new Pair<>("answer", 42);
entry.getT1(); // "answer"
entry.getT2(); // 42

Serializable variants live under com.svenruppert.functional.model.serial.

Pattern matching with Case

Fri, 15 May 2026 00:00:00 +0000

Coming soon.

Checked Functions

Mon, 01 Jan 0001 00:00:00 +0000

Standard Function, BiFunction, Consumer and friends cannot throw checked exceptions without wrapping. functional-reactive ships drop-in replacements that can:

CheckedFunction<T, R>
CheckedBiFunction<T1, T2, R>
CheckedTriFunction<T1, T2, T3, R>
CheckedConsumer<T>, CheckedSupplier<T>, CheckedPredicate<T>, CheckedExecutor

CheckedFunction<String, Integer> parse = Integer::parseInt;
Result<Integer> r = parse.apply("42"); // Success(42)
Result<Integer> r2 = parse.apply("oops"); // Failure("...")

Every checked function returns a Result, so failures travel through your pipeline without explicit try/catch.

Memoizing expensive computations

Fri, 15 May 2026 00:00:00 +0000

Coming soon.

CompletableFutureQueue

Mon, 01 Jan 0001 00:00:00 +0000

CompletableFutureQueue
 .define((String s) -> s.length())
 .thenCombineAsync(len -> len * 2)
 .apply("hello") // CompletableFuture<Integer>
 .thenAccept(System.out::println); // 10

Each step runs on the common ForkJoinPool unless you pass an explicit Executor.

Working with checked exceptions

Fri, 15 May 2026 00:00:00 +0000

Coming soon.

Case

Mon, 01 Jan 0001 00:00:00 +0000

Case lets you express conditional logic as data — each branch is a predicate plus a value (or value-supplier), evaluated in order.

String label = Case.match(score)
 .of(s -> s >= 90, "A")
 .of(s -> s >= 80, "B")
 .of(s -> s >= 70, "C")
 .orElse("F");

No fall-through, no boilerplate, fully type-safe.

Memoizer

Mon, 01 Jan 0001 00:00:00 +0000

Memoizer wraps a pure Function, BiFunction or TriFunction so subsequent calls with the same arguments are served from cache.

Function<Integer, Long> slowFib = Memoizer.memoize(n ->
 n < 2 ? n : slowFib.apply(n-1) + slowFib.apply(n-2));

slowFib.apply(40); // fast — even though the body is naïve

Memoization only makes sense for pure functions. Caching the result of a function with side-effects (logging, DB writes) will silently change behaviour.

Transformations

Mon, 01 Jan 0001 00:00:00 +0000

Static helpers for working with multi-argument functions:

curryBiFunction() / unCurryBiFunction()
curryTriFunction() / unCurryTriFunction()
curryCheckedBiFunction() / unCurryCheckedBiFunction()
iteratorToStream()

BiFunction<Integer, Integer, Integer> add = Integer::sum;
Function<Integer, Function<Integer, Integer>> curried =
 Transformations.<Integer, Integer, Integer>curryBiFunction().apply(add);

curried.apply(2).apply(3); // 5

Utility Functions

Mon, 01 Jan 0001 00:00:00 +0000

The com.svenruppert.functional package collects small, focused utilities:

StringFunctions — string transformations ported from Strman.
StreamFunctions — curried predicates and stream filters.
ExceptionFunctions — message() and toStackTraceStream().
Converting — convertToString / Integer / Double returning Result.
SystemProperties — typed access to system properties.

Release 06.01.01

Thu, 23 Apr 2026 00:00:00 +0000

The 06.01.01 release continues the 06.x line under the com.svenruppert namespace.

Highlights

Updated parent BOM to com.svenruppert:dependencies:06.01.01.
All previous functionality from the 03.x rename is stable.

Upgrading from 03.x

Just bump the version — no source changes required.

<dependency>
 <groupId>com.svenruppert</groupId>
 <artifactId>functional-reactive</artifactId>
 <version>06.01.01</version>
</dependency>

For the full history, see the README.

Functional Reactive Lib

Error handling with Result

The problem

The Result way

Getting Started

Add the dependency

Your first Result

Next steps

Result

Construction

Transformations

Combinators

Terminal operations

Async pipelines with CompletableFutureQueue

Tuples (Pair…Sept)

Pattern matching with Case

Checked Functions

Memoizing expensive computations

CompletableFutureQueue

Working with checked exceptions

Case

Memoizer

Transformations

Utility Functions

Release 06.01.01

Highlights

Upgrading from 03.x

Your first `Result`