Forth Online Compiler

Forth doesn't look like most programming languages. There are no parentheses wrapping function arguments. No infix operators. You push values onto a stack, then apply operations that pop values off and push results back. It uses reverse Polish notation -- 3 4 + instead of 3 + 4. This minimal design made Forth popular in embedded systems and firmware where every byte of memory counted.

Why run Forth in the browser?

Setting up a local Forth environment (gforth, SwiftForth, etc.) isn't hard, but it's an extra step when you just want to test how a word definition works or remind yourself of stack manipulation order. A Forth online compiler lets you open a tab and start coding immediately.

Good use cases:

• Learning stack-based programming for the first time
• Prototyping a custom word before adding it to a larger Forth system
• Sharing Forth snippets with others who don't have a local setup

Stack operations and defining a word

This example defines a word that computes the square of a number, then uses it:

: SQUARE ( n -- n^2 )
  DUP * ;

: CUBE ( n -- n^3 )
  DUP SQUARE * ;

5 SQUARE . CR
3 CUBE . CR

." Stack-based computing at its simplest" CR

The : SQUARE line creates a new word. DUP duplicates the top of the stack, * multiplies the top two values. That's it -- no variable declarations, no return statements. The comment ( n -- n^2 ) is a stack effect diagram showing what goes in and what comes out, which is a convention in Forth programming.

OneCompiler for Forth

OneCompiler's Forth environment handles standard Forth syntax and gives you instant output. It's a clean way to experiment with stack manipulation, word definitions, and control structures without wrestling with a local install.

Give it a try: Forth Online Compiler on OneCompiler