Hello, World
." Hello, World!" crmain.fth
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main.fth · output appears here
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Forth 0.7.3Readymain.fthLn 1, Col 1Spaces: 4UTF-8
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main.fth · output appears here
Press Run to execute
Output streams here as your program runs.
Forth is a stack-based, concatenative programming language built around an explicit data stack and a dictionary of words. Instead of named variables and infix expressions, you push values onto the stack and apply words that consume and produce stack items, using postfix (reverse Polish) notation. CompileBytes runs GNU Forth (gforth) 0.7.3, a fast and portable Forth system with an interactive interpreter and compiler.
Programming in Forth means defining new words from existing ones, growing the language toward your problem. A word definition starts with : and ends with ; and runs by manipulating the stack. This minimal, extensible model historically made Forth popular for embedded systems, bootloaders, and resource-constrained environments. Its interactivity and tiny footprint make it an excellent vehicle for learning how stacks and threaded code work.
main.fth is the entry point for each run.
Use the Input panel to pipe standard input to your program when it needs data.
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." Hello, World!" cr: square ( n -- n*n ) dup * ;
5 square . cr2 3 + . cr
10 4 - . cr: counts ( -- )
5 0 do i . loop cr ;
counts: sign ( n -- )
dup 0 > if ." positive" else ." non-positive" then drop cr ;
5 sign
-3 sign42 constant answer
variable total
10 total !
answer total @ + . cr: sum ( n -- sum )
0 swap 1+ 1 do i + loop ;
5 sum . cr: fact ( n -- n! )
dup 1 > if dup 1- recurse * else drop 1 then ;
5 fact . cr1 2 3 .s cr
swap .s cr
over .s crThe editor uses Monaco, the engine behind VS Code, with language-aware editing tools and familiar keyboard controls.
Type or paste your code into the editor, then click Run (or press Ctrl/Cmd + Enter) to execute it.
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Forth is one of 46 single-file compiler scratchpads. Each run submits only main.fth; local sibling-file imports are not enabled.
Linked-project languages (23): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Bun, Objective-C.
Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme.
Download file exports the active Forth source file.