In this section, we will write our first F# program. This will help you get familiar with the basic structure of an F# application and understand how to compile and run it.

• Understand the basic structure of an F# program.
• Write a simple F# program.
• Compile and run the F# program.

An F# program typically consists of:

1. Modules: Containers for code, similar to namespaces in other languages.
2. Functions: The primary building blocks of F# programs.
3. Expressions: Code that produces a value.

Here is a simple example of an F# program:

• module HelloWorld: Defines a module named HelloWorld.
• let sayHello name = ...: Defines a function sayHello that takes a parameter name and prints a greeting.
• sayHello "World": Calls the sayHello function with the argument "World".

Let's write a simple F# program that prints "Hello, F# World!" to the console.

1. Create a New File: Open your text editor or IDE and create a new file named Program.fs.

2. Write the Code: Enter the following code into Program.fs:

   // Define the main module
   module Program
   
   // Define the main function
   [<EntryPoint>]
   let main argv =
       printfn "Hello, F# World!"
       0 // Return an integer exit code
   

3. Explanation:

   • module Program: Defines a module named Program.
   • [<EntryPoint>]: Marks the main function as the entry point of the program.
   • let main argv = ...: Defines the main function, which takes an array of strings argv (command-line arguments) and returns an integer exit code.
   • printfn "Hello, F# World!": Prints "Hello, F# World!" to the console.
   • 0: Returns 0 as the exit code, indicating that the program finished successfully.

1. Open a Terminal: Open your terminal or command prompt.

2. Navigate to the Directory: Navigate to the directory where you saved Program.fs.

3. Compile the Program: Run the following command to compile the program:

   dotnet fsi Program.fs
   

4. Run the Program: If you used dotnet fsi, the program will run immediately after compilation, and you should see the output:

   Hello, F# World!
   

1. Open Visual Studio Code: Open Visual Studio Code and open the folder containing Program.fs.

2. Install Ionide Extension: If you haven't already, install the Ionide extension for F#.

3. Open the Integrated Terminal: Open the integrated terminal in Visual Studio Code.

4. Compile and Run: Use the terminal to run the following command:

   dotnet fsi Program.fs
   

5. View the Output: You should see the output in the terminal:

   Hello, F# World!
   

Write an F# program that prints "Welcome to F# Programming!" to the console.

1. Create a New File: Create a new file named Welcome.fs.

2. Write the Code: Enter the following code into Welcome.fs:

   // Define the main module
   module Welcome
   
   // Define the main function
   [<EntryPoint>]
   let main argv =
       printfn "Welcome to F# Programming!"
       0 // Return an integer exit code
   

3. Compile and Run: Use the terminal to compile and run the program:

   dotnet fsi Welcome.fs
   

4. Expected Output:

   Welcome to F# Programming!
   

In this section, you learned how to write, compile, and run a simple F# program. You now understand the basic structure of an F# application, including modules, functions, and expressions. This foundational knowledge will be crucial as you progress through the course and tackle more complex topics.

Next, we will dive into core concepts such as data types and variables, which are essential for writing more sophisticated F# programs.