DarkPeak.Functional

A functional programming library for .NET providing monadic types and railway-oriented programming patterns.

Core Types

• Option<T> — Eliminates null reference exceptions with explicit presence/absence
• Result<T, TError> — Railway-oriented error handling without exceptions
• Either<TLeft, TRight> — Symmetric dual-value type for branching logic
• OneOf<T1, ..., Tn> — Discriminated unions with 2-8 explicitly typed cases
• Validation<T, TError> — Accumulates multiple errors instead of short-circuiting

Resilience & Caching

• Retry — Configurable retry policies with backoff strategies
• Circuit Breaker — Prevents cascading failures by short-circuiting requests to failing dependencies
• Memoize — Function caching with TTL, LRU eviction, and distributed cache support

Integration Packages

• DarkPeak.Functional.Http — Wraps HttpClient in Result<T, Error> for exception-free HTTP communication
• DarkPeak.Functional.AspNet — Converts Result<T, Error> to IResult and ProblemDetails for minimal APIs
• DarkPeak.Functional.Redis — Redis distributed cache provider for Memoize and MemoizeResult
• DarkPeak.Functional.Dapper — Wraps Dapper queries and commands in Result<T, Error> with typed database error mapping
• DarkPeak.Functional.EntityFramework — Wraps EF Core operations in Result<T, Error> with typed error handling
• DarkPeak.Functional.HealthChecks — Exposes circuit breaker and cache provider status via ASP.NET Core IHealthCheck implementations
• DarkPeak.Functional.Mediator — Integrates Result<T, Error> with Mediator for source-generated CQRS pipelines

Quick Start

using DarkPeak.Functional;

// Option — no more nulls
Option<string> name = Option.Some("Alice");
var greeting = name.Map(n => $"Hello, {n}!");

// Result — railway-oriented programming
Result<int, ValidationError> parsed = Result.Success<int, ValidationError>(42);
var doubled = parsed.Map(x => x * 2);

// OneOf — multiple valid shapes
OneOf<string, int, bool> response = true;
var description = response.Match(
    text => text,
    number => number.ToString(),
    flag => flag ? "enabled" : "disabled");

// Fluent chaining
var result = await Option.Some("42")
    .ToResult(new ValidationError { Message = "Missing" })
    .Map(int.Parse)
    .Map(x => x * 2)
    .Match(
        success: x => $"Result: {x}",
        failure: e => $"Error: {e.Message}");

Installation

dotnet add package DarkPeak.Functional

Learn More

• Getting Started — Installation, concepts, and first steps
• OneOf — Discriminated unions with 2-8 cases and Either interop
• Orchestration — Combining Validation and Result pipelines in real-world scenarios
• Example: Blazor Form — Using Validation in a Blazor component with inline field errors
• API Reference — Full API documentation generated from source