Get started with F# in Visual Studio
F# is supported in the Visual Studio integrated development environment (IDE).
To begin, ensure that you have Visual Studio installed with F# support.
Create a console application
One of the most basic projects in Visual Studio is the console app. Here's how to create one:
Open Visual Studio 2019.
On the start window, choose Create a new project.
On the Create a new project page, choose F# from the Language list.
Choose the Console App (.NET Core) template, and then choose Next.
On the Configure your new project page, enter a name in the Project name box. Then, choose Create.
Visual Studio creates the new F# project. You can see it in the Solution Explorer window.
Write the code
Let's get started by writing some code. Make sure that the Program.fs file is open, and then replace its contents with the following:
module HelloSquare
let square x = x * x
[<EntryPoint>]
let main argv =
printfn "%d squared is: %d!" 12 (square 12)
0 // Return an integer exit code
The previous code sample defines a function called square that takes an input named x and multiplies it by itself. Because F# uses Type inference, the type of x doesn't need to be specified. The F# compiler understands the types where multiplication is valid and assigns a type to x based on how square is called. If you hover over square, you should see the following:
val square: x: int -> int
This is what is known as the function's type signature. It can be read like this: "Square is a function that takes an integer named x and produces an integer". The compiler gave square the int type for now.
Another function, main, is defined, which is decorated with the EntryPoint attribute. This attribute tells the F# compiler that program execution should start there. It follows the same convention as other C-style programming languages, where command-line arguments can be passed to this function, and an integer code is returned (typically 0).
It is in the entry point function, main, that you call the square function with an argument of 12. The F# compiler then assigns the type of square to be int -> int (that is, a function that takes an int and produces an int). The call to printfn is a formatted printing function that uses a format string and prints the result (and a new line). The format string, similar to C-style programming languages, has parameters (%d) that correspond to the arguments that are passed to it, in this case, 12 and (square 12).
Run the code
You can run the code and see the results by pressing Ctrl+F5. Alternatively, you can choose the Debug > Start Without Debugging from the top-level menu bar. This runs the program without debugging.
The following output prints to the console window that Visual Studio opened:
12 squared is: 144!
Congratulations! You've created your first F# project in Visual Studio, written an F# function that calculates and prints a value, and run the project to see the results.
Next steps
If you haven't already, check out the Tour of F#, which covers some of the core features of F#. It provides an overview of some of the capabilities of F# and ample code samples that you can copy into Visual Studio and run.
