Forth Programming Language: How to Write and Run Your First Program (Step-by-Step Guide)

Hello, fellow Forth enthusiasts! In this blog post, Forth Programming First Program &#

8211; I will introduce you to the basics of writing and running your first program in the Forth programming language. Forth is a stack-based, extensible language known for its simplicity and efficiency. It is widely used in embedded systems, robotics, and real-time applications. In this post, I will guide you through writing your first Forth program, understanding its structure, and executing it step by step. You will learn how Forth handles input, output, and basic operations. By the end, you’ll be ready to write and run your own Forth programs with confidence. Let’s get started!

Introduction to Writing and Executing Your First Program in Forth Language

Forth is a unique and powerful stack-based programming language known for its efficiency and flexibility. It is widely used in embedded systems, robotics, and low-level programming due to its minimalistic yet extensible nature. In this post, we will explore the basics of writing and executing your first program in Forth. You’ll learn how Forth processes commands, works with the stack, and interprets instructions interactively. We will start by setting up a Forth environment, writing simple programs, and running them step by step. By the end of this guide, you’ll have a solid foundation to begin coding in Forth confidently. Let’s dive in!

What is Writing and Executing Your First Program in Forth Programming Language?

Forth is a stack-based, interactive, and extensible programming language widely used in embedded systems, robotics, and low-level programming. Unlike traditional languages, Forth operates using a stack to manage data, making it both efficient and unique. In this guide, we will walk you through the process of writing and executing your first Forth program, explaining key concepts along the way. Whether you are a beginner or transitioning from another programming language, this step-by-step guide will help you get started with Forth programming.

Setting Up the Forth Environment

Before writing your first program, you need a Forth development environment. Here’s how to set it up:

Option 1: Using Gforth (Recommended for Beginners)

Gforth is one of the most widely used implementations of Forth and works on Windows, Linux, and macOS.

Installing Gforth:

• Windows: Download and install Gforth from https://www.gnu.org/software/gforth/.
• Linux/macOS: Open a terminal and run:

sudo apt install gforth  # For Ubuntu/Debian
brew install gforth      # For macOS (Homebrew)

• After installation, verify it by typing gforth in the terminal.

Option 2: Using Online Forth Interpreters

If you don’t want to install anything, you can try online interpreters like:

• Try It Online (TIO): https://tio.run
• Forth Online Compiler: https://repl.it

Understanding the Basics of Forth

Key Features of Forth:

• Stack-Based: Data is stored in a stack, and operations are performed using push/pop.
• Interactive: Commands can be entered and executed immediately in the interpreter.
• Extensible: Users can define their own commands (called “words”).

Basic Syntax:

• Forth operates on a Reverse Polish Notation (RPN) style, meaning operators follow operands.
• Example: Instead of 2 + 3, you write 2 3 +.

Executing Commands in the Forth Interpreter:

Open Gforth and type:

2 3 + .

Output:

5

• 2 3 + → Pushes 2 and 3 to the stack, then adds them.
• . → Prints the result (5).

Writing Your First Forth Program

Let’s write a simple “Hello, World!” program.

Step 1: Open Gforth

Type gforth in your terminal or command prompt to start the interpreter.

Step 2: Write a Simple Forth Program

: hello  ." Hello, World!" ;

• : hello → Defines a new word (function) named hello.
• ." Hello, World!" → Prints “Hello, World!” to the screen.
• ; → Ends the word definition.

Step 3: Execute the Program

After defining hello, run it by typing:

hello

Output:

Hello, World!

Understanding Forth’s Stack Operations

Since Forth is stack-based, let’s explore some simple stack operations.

Pushing and Popping Values

10 20 30  .s

Output:

<3> 10 20 30

• 10 20 30 → Pushes numbers onto the stack.
• .s → Prints the stack contents (<3> means three items are in the stack).

Performing Arithmetic in Forth

5 10 + .

Output:

15

• 5 10 + → Adds 5 and 10, leaving 15 on the stack.
• . → Prints the result (15).

Swapping Values on the Stack

1 2 swap .s

Output:

<2> 2 1

• swap exchanges the top two elements on the stack.

Writing a Simple Loop in Forth

Let’s write a loop to print numbers from 1 to 5.

: count  5 1 do i . loop ;

• : count → Defines a new word (function) named count.
• 5 1 do → Starts a loop from 1 to 5.
• i . → Prints the current loop index (i).
• loop → Ends the loop.

Run the Function:

count

Output:

1 2 3 4 5

Creating and Using Variables in Forth

Forth allows you to define variables using variable and store values using ! (store) and @ (fetch).

variable num
10 num !
num @ .

Output:

10

• variable num → Defines a variable num.
• 10 num ! → Stores 10 in num.
• num @ . → Fetches the value of num and prints it.

Defining and Using Custom Words (Functions) in Forth

Forth allows you to create custom commands, called words, using : <name> ... ;.

: square ( n -- n^2 ) dup * ;
5 square .

Output:

25

• : square → Defines a word square.
• ( n -- n^2 ) → Comment notation showing input (n) and output (n^2).
• dup * → Duplicates n and multiplies it (n * n).
• 5 square . → Calls square with 5, prints 25.

Saving and Running a Forth Program from a File

Instead of entering commands interactively, you can write a Forth script in a file and run it.

Step 1: Create a File

Create a new file hello.fth and add:

: hello  ." Hello from Forth!" ;
hello

Step 2: Run the Script

In the terminal, execute:

gforth hello.fth

Output:

Hello from Forth!

• Congratulations! 🎉 You have successfully written and executed your first program in Forth Programming Language. You learned how to:
  • Install and set up Forth.
  • Write and run simple Forth commands.
  • Work with the stack and arithmetic operations.
  • Define and use loops, variables, and custom words.
  • Execute Forth programs from a file.

With this knowledge, you can now explore more advanced concepts like conditionals, memory management, and interactive debugging. Keep experimenting with Forth and happy coding!