DotNetFunctional.Maybe

An Option monad for C# with LINQ support and rich fluent syntax.

Installation

DotNetFunctional.Maybe can be installed using the NuGet command line or the NuGet Package Manager in Visual Studio.

PM> Install-Package DotNetFunctional.Maybe

Example

First, you will need to add the following using statement:

using DotNetFunctional.Maybe;

Lift values

Both reference type and value type objects can be lifted by using the Maybe.Lift static method:

Maybe<string> maybeHello = Maybe.Lift("hello");
Maybe<string> maybeTen = Maybe.Lift(10);

Computing using query expressions

Maybe<string> maybeHello = Maybe.Lift("hello");
Maybe<string> maybeNothing = Maybe<string>.Nothing;

var maybeConcat = from hello in maybeHello
                  from nothing in maybeNothing
                  select hello + nothing;

if(!maybeConcat.HasValue)
{
    Console.WriteLine("One of the strings was bad, could not concat");
}

LINQ will short-circuit any expression if there is a Maybe<T>.Nothing at any point in the computation.

Unwrapping

Values from Maybe<T> instance can be unwrapped directly in a safe way by using the Maybe<T>#OrElse extension method. The method allows you to provide a fallback value_ in case that the wrapper contains nothing. The fallback value can be directly provided or by a delegate that is lazily invoked.

Maybe<string> maybeNothing = Maybe<string>.Nothing;

string directValue = maybeNothing.OrElse("something");
string delegateValue = maybeNothing.OrElse(() => "something lazy");

Pattern matching

A pattern match like method is exposed:

Maybe<string> maybeHello = Maybe.Lift("hello");
Maybe<string> maybeTen = Maybe<int>.Nothing;

// Yield "Hello matched"
string hello = maybeHello.Match(val => $"Hello matched!", string.Empty);
// Yields 10
int ten = maybeTen.Match(val => val, 10);

Side-Effects

To perform side effects, Maybe<T> exposes a Tap<T>(somethingFn: Action<T>, nothingFn: Action) method. It takes 2 delegates, invokes the according one depending on if the wrapper has something or not and returns the original wrapper.

strig value = ...
Maybe<string> wrapper = Maybe.Lift(...)
                        .Tap(val => Console.WriteLine(value), () => Console.WriteLine("Nothing"));

Other projects

Check out some of my other C# projects:

• DotNetFunctional.Maybe: An Option type monad for C# with LINQ support and rich fluent syntax.
• Specimen: Basic contract and abstract implementation of the specification pattern.