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LanguageExt.Core

Option monads support either an A (success) value, or a None (no-value) option. You can think of this as an alternative to using null to represent a lack of a value. null unfortunately still allows you to . into the interface of the decalred type, which means there's a ticking time-bomb in every reference type.

C# does now have the nullable references feature, which goes some way to removing the need for an optional type, however there's still edge cases that mean the reference types are problematic. It's also useful to build generic types and say this is an Option<A> - I don't care if it's a value-type or reference-type, it's optional.

And finally, there's the automatic checking of None values when using Option<A> in LINQ expressions, or if you call Map. This makes working with optional values, and the implications for all of the code that works with it, fully declarative.

Here we have three flavours of Option:

1. Option<A> the default optional monad. It does not allow null in its Some case.
2. OptionUnsafe<A> as above, but it does allow null in its Some case.
3. OptionAsync<A> is equivalent to Task<Option<A>>, but much more convenient to use, especially with LINQ expressions

You can construct a Some using the constructor functions in the Prelude:

Option<int> ma = Some(123);
Option<int> mb = None;