Execute F# code in C# Program

Intro

Functional programming is getting more and more attention lately, mostly because GPU’s and multi-core processors all use parallel execution for performance and the fact that functional languages encourage the use of immutable data, that prevents many errors in writting parallel code. Many modern OO languages have implemented a way of doing functional proggraming like LINQ in C#.

Benefits of Functional Programming

Functional programming is very appealing due to:

• Convenience: type definitions, comparisons, states, equality, etc are much simpler in functional languages.
• Concurrency: asynchronous programming is directly supported.
• Brevity: functional code is more concise.

Problem

This all sounds good but how can we use this in our C# programs?

F# and .NET

The greatest benefit from F#, is F# being CLR language and with that you can use everything from the appropriate .NET framework. Here I will create simple VS solution that show how F# is used in a C# application.

Solution

I will create simple C# console application, with separate domain library, and F# class library.

C# Domain Library

• Create new solution and add C# Class Library targeting .NET Standard 2.0 and name it Domain.
• Create new class Person.cs.

public class Person {
    public string Name { get; set; }
    public int Height { get; set; }
    public int Years { get; set; }

    public Person(string name, int height, int years) {
        Name = name;
        Height = height;
        Years = years;
    }
}

This is all we are going to need.

F# Class Library

• Add new F# Class Library project to the solution named FSharp.
• Add reference to the Domain project.
• Lets write some functions in Library.fs.

First define the namespace:

namespace FSharp

Then create module:

module Say =

Now write some functions:

// returning string
let hello name =
    "Hello " + name

// calculating average height from Person list
let avgHeight xs =
    let sum = xs |> List.sumBy (fun (x : Person) -> x.Height) |> double
    let length = List.length xs |> double
    sum / length

C# Console Application

Let’s try out the F# class project.

• Create C# Console Application.
• Add reference to Domain and FSharp projects.

Lets try hello function (w/o parameters):

var helloFsharp = FSharp.Say.hello("C#");
Console.WriteLine(helloFsharp);
// prints 'Hello C#'

Now avgHeight that needs list of Person objects. First lets initialize list of Person objects:

var personList = new List<Person> {
    new Person("Person  1", 160, 22),
    new Person("Person  2", 172, 45),
    new Person("Person  3", 196, 63),
    new Person("Person  4", 154, 18),
    new Person("Person  5", 178, 64),
    new Person("Person  6", 187, 35),
    new Person("Person  7", 169, 27),
    new Person("Person  8", 186, 45),
    new Person("Person  9", 167, 36),
    new Person("Person 10", 190, 65),
};

If we want to send this list as argument, first we need to convert it to F# list (FSharpList). This is very easy since there is package (Microsoft.FSharp.Collections.ListModule) in C# that do this:

// converting list
var fsharpList = ListModule.OfSeq(personList);

And now we can call the function for a result:

var result = FSharp.Say.avgHeight(fsharpList);
// result: 175.9

Conclusion

It is very easy to use F# in C# programs, and there are some nice reasons why you should. Next time you encounter some problems that are easier to solve using functional programming, try F#.

Info

You can download the code from GitHub, or try to follow this post step by step.

Open on GitHub

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