FunctionalDotNet

A functional programming toolkit for C#, plus a growing set of example projects that show what idiomatic functional code looks like across different kinds of .NET applications.

The repository has two faces:

1. FunctionalDotNet — a class library that provides the building blocks the standard library doesn't: Option, Either, Validation, function composition helpers, and the rest of the FP toolkit. It is being built from the ground up here, exercise by exercise, and is intended to ship as a NuGet package.
2. Example projects — small .NET applications (Web API, Windows Service, desktop app, etc.) that consume FunctionalDotNet and demonstrate functional patterns in realistic settings, not just in unit tests.

This is a learning resource and a reference. It's open source, and contributions are welcome.

Why build our own library?

Most C# functional libraries trace back to Enrico Buonanno's Functional Programming in C# and its companion LaYumba.Functional. Those are excellent. But building the toolkit ourselves, in the open, has its own value:

• Every type comes with the reasoning behind it, not just the API. The library doc explains why Option<T> looks the way it does, why Bind has the signature it has, why Validation<T> accumulates errors instead of short-circuiting.
• It forces a bottom-up understanding of the abstractions instead of treating them as primitives.
• It gives a single, consistent surface area to use across all the example projects.

Repository layout

FunctionalDotNet/              the library (class library, net10.0)
FunctionalDotNet.Tests/        xUnit v3 tests for the library
docs/
    functional-programming-intro.md   paradigm-level introduction to FP
    functionaldotnet-library.md       the library's design notes and usage
FunctionalDotNet.slnx          solution file (slnx format)

Example projects (Web API, Windows Service, desktop app, etc.) will be added alongside the library and listed here as they land.

Requirements

• .NET 10 SDK

Getting started

git clone https://github.com/NGDeveloper125/FunctionalDotNet.git
cd FunctionalDotNet
dotnet build
dotnet test --solution FunctionalDotNet.slnx

Documentation

• Introduction to functional programming — the paradigm-level concepts the library is built on: pure functions, immutability, higher-order functions, Option / Either, monoids and monads.
• FunctionalDotNet library — the library's own documentation: design decisions, the public API as it grows, and usage examples.

Status

Early. The solution and project skeletons are in place; the library is empty and we are about to start adding types one at a time, each with its own tests and documentation.

Contributing

Contributions of all sizes are welcome — a new library type, a new example project, a cleaner implementation, a typo fix, or a suggestion. Open an issue or a pull request.

The only soft rule is: favour clarity over cleverness, and lean into the functional approach rather than "C# with lambdas".