Mackiovello.Maybe 1.0.0

.NET Standard 2.0
Install-Package Mackiovello.Maybe -Version 1.0.0
dotnet add package Mackiovello.Maybe --version 1.0.0
<PackageReference Include="Mackiovello.Maybe" Version="1.0.0" />
For projects that support PackageReference, copy this XML node into the project file to reference the package.
paket add Mackiovello.Maybe --version 1.0.0
The NuGet Team does not provide support for this client. Please contact its maintainers for support.
#r "nuget: Mackiovello.Maybe, 1.0.0"
#r directive can be used in F# Interactive, C# scripting and .NET Interactive. Copy this into the interactive tool or source code of the script to reference the package.
// Install Mackiovello.Maybe as a Cake Addin
#addin nuget:?package=Mackiovello.Maybe&version=1.0.0

// Install Mackiovello.Maybe as a Cake Tool
#tool nuget:?package=Mackiovello.Maybe&version=1.0.0
The NuGet Team does not provide support for this client. Please contact its maintainers for support.


Build Status

Option types for C# with LINQ support and rich fluent syntax for many popular uses


All these examples require that you have the following using statement:

using Mackiovello.Maybe

Computing on maybe types

Maybe<string> maybeGood = "hello".ToMaybe();
Maybe<string> maybeJunk = Maybe<string>.Nothing;

var concat = from good in maybeGood
             from junk in maybeJunk
             select good + junk;

if (concat.IsNothing())
  Console.WriteLine("One of the strings was bad, could not concat");

LINQ terminates the computation if there's a Nothing at any point in the computation.

Running a computation with a maybe type:

string nullString = null;

nullString.ToMaybe().Do(str => 
  // str will never be null, ToMaybe guards against null and Do unwraps the value


You can check a condition on a maybe type and guard against them:

string name = "Bill Casarin";
Maybe<string> maybeName = from n in name.ToMaybe()
                          where n.StartsWith("Bill")
                          select n;

If the name didn't start with Bill, maybeName would be Maybe<string>.Nothing

Maybe coalescing

Maybe has an operator similar to the null coalescing operator ??. We achieve optional short-circuit evaluation with lambdas:

Maybe<string> name1 = Maybe<string>.Nothing;
Maybe<string> name2 = "Some Name".ToMaybe();

Maybe<string> goodNameLazy = name1.Or(() => name2);
// this works too:
Maybe<string> goodName = name1.Or(name2);
// and this:
Maybe<string> goodName = name1.Or("goodName");

You can also convert value-kinded maybe types to Nullable<T>s:

Maybe<int> maybeNumber = Maybe<int>.Nothing;
Maybe<int> maybeAnotherNumber = (4).ToMaybe();

int? ok = maybeNumber.ToNullable() ?? maybeAnotherNumber.ToNullable();

Extracting values

Sometime you want to pull out a value with a default value in case of Nothing:

Maybe<string> possibleString = Maybe<string>.Nothing;
string goodString = possibleString.OrElse("default");

The default parameter can also be lazy:

string goodString = possibleString.OrElse(() => doHeavyComputationForString());

Or you can throw an exception instead:

string val = null;
  val = (Maybe<string>.Nothing).OrElse(() => new Exception("no value"));
catch (Exception) 
  // exception will be thrown

Or, finally, you can just get the default value for that type:

string val = maybeString.OrElseDefault();

Why not use Nullable<T> instead?

Nullable<T> only works on value types. Maybe<T> works on both value and reference types. It also has LINQ support.

More interesting examples

Getting the first element of a list

public static Maybe<T> Head<T>(this IEnumerable<T> xs) 
  foreach(var x in xs)
    return x.ToMaybe();
  return Maybe<T>.Nothing;

Now lets get a bunch of heads!

var result = from h1 in list1.Head()
             from h2 in list2.Head()
             from h3 in list3.Head()
             select ConsumeHeads(h1, h2, h3);

ConsumeHeads will never run unless all Head() calls return valid results.


Here's a function for getting a value out of a dictionary:

public static Maybe<T2> Lookup<T, T2>(this IDictionary<T, T2> d, T key) 
  var getter = MaybeFunctionalWrappers.Wrap(d.TryGetValue);
  return getter(key);


public static Maybe<int> ParseInt(string s) 
  var parser = MaybeFunctionalWrappers.Wrap(int.TryParse);
  return parser(s);

Lookup + Parsing!

var parsedFromDict = from val in d.Lookup("key")
                     from parsedVal in ParseInt(val)
                     select parsedVal;
Product Versions
.NET net5.0 net5.0-windows net6.0 net6.0-android net6.0-ios net6.0-maccatalyst net6.0-macos net6.0-tvos net6.0-windows
.NET Core netcoreapp2.0 netcoreapp2.1 netcoreapp2.2 netcoreapp3.0 netcoreapp3.1
.NET Standard netstandard2.0 netstandard2.1
.NET Framework net461 net462 net463 net47 net471 net472 net48
MonoAndroid monoandroid
MonoMac monomac
MonoTouch monotouch
Tizen tizen40 tizen60
Xamarin.iOS xamarinios
Xamarin.Mac xamarinmac
Xamarin.TVOS xamarintvos
Xamarin.WatchOS xamarinwatchos
Compatible target framework(s)
Additional computed target framework(s)
Learn more about Target Frameworks and .NET Standard.
  • .NETStandard 2.0

    • No dependencies.

NuGet packages

This package is not used by any NuGet packages.

GitHub repositories

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Version Downloads Last updated
1.0.0 55,427 7/3/2018