Functional Linq tips for senior C# developers

Here are some basic tips for senior developers, who want to understand, and potentially use Linq native query syntax in their code, beyond the standard IEnumerable implementation.

1. Linq support for select

Did you know that if you implement Select method in any type you can use the from …in …select Linq syntax ???

I will take a random data straucture like this Func<List<int>> and add linq query support. First of all i can make it into a functor and use Linq’s select by adding this extension method :

public static  Func<List<T1>>  Select<T,T1> 
(this Func<List<T>> x, Func<T,T1> func) 
 
{                         
 return ()=>(x()).Select(i=>func(i)).ToList();                         }

and then its perfectly valid to write this :

Func<List<int>> f1 = ()=>new List<int>{7,8,9,2};                           var r = from c in f1 select c;

Linq Support Functors — Functors | C# Online Compiler | .NET Fiddle

As a summary if i get a data structure and add a Mapping method then this is a functor

Data Structure + Select (aka Map) Method = A Functor

You can see more here about functor in c# functional programming.

2. Linq support for Filtering

In C# if you implement a Method

public Functor<T> Where(Func<T, bool> predicate)

you can use the from …in …where …select Linq syntax . If we continue extending our previous example, by adding this :

public static Func<List<T>> Where<T>
(this Func<List<T>> x,
Func<T, bool> predicate)
{
   return () => x().Where(predicate).ToList();
}

we can write now

var filterResult = from c in f1 where c ==2 select c ;

3. Linq Support For Monads

Now in order to write something like this

Func<List<T>> monadincResult =
 from x in f1 
 from y in f2
 where x ==2
 select x+ y;

which means we combine two of our functors into a single one, we must provide a “simple” method that will do this mixing. In Linq this is called SelectMany. By providing a SelectMany the functor now has been upgraded practically to a Monad, as far as we are concerned.

Data Structure + Select (aka Map) +SelectMany (aka Bind) = Monad

i did this it for this random Func<List<int>> functor that now became this “lazy list monad” for lack of better wording. It looks like that :

you can try it, or play around, in this .net fiddle .

Linq Support Functors - Monads | C# Online Compiler | .NET Fiddle

Conclusion :

I am not saying that you have to, or even need to use Linq syntax in your project data structures. But as a senior c# developer, one must be familiar with this concept and have an advanced understanding on how Linq works, also it offers a fundamental understanding of Functors and Monads .

Its very useful to know that you can make up a monad by just Implementing the SelectMany method, which is not always easy.

https://leanpub.com/c/functionalprogrammingincwithcategories

you can learn more about Functors and monads here :

Monads in OOP with C#

Introduction to Functors in C#

feel free to connect with me in LinkedIn

Dimitris Papadimitriou - Software Engineer