100hellos/factor repository overview

⁠Hello World! From factor.

Language page⁠ — context, influences, and learning notes on the 100hellos site.

Source on GitHub⁠ (100hellos/factor)

⁠Trying it

docker run --rm --platform="linux/amd64" 100hellos/factor:latest

⁠Modifying it

Read the repo README⁠, or fork the project⁠ and customize it.

For an interactive shell:

docker run --rm --platform="linux/amd64" --entrypoint="" -it 100hellos/factor:latest zsh

⁠Factor

Factor is a concatenative, stack-based programming language inspired by Forth and Lisp. It was designed by Slava Pestov and features powerful metaprogramming capabilities, a rich standard library, and an elegant object system.

⁠About Factor

Factor is a dynamic, stack-based language with powerful metaprogramming features. It combines the simplicity of stack-based programming with modern language features like:

• Dynamic typing with optional static type inference
• Powerful metaprogramming through quotations and combinators
• Rich standard library including GUI frameworks, web development tools, and more
• Interactive development with a sophisticated listener (REPL)
• Object-oriented programming with generic functions and method dispatch

⁠The Stack-Based Paradigm

In Factor, computation is performed by manipulating a data stack. Functions (called "words" in Factor) consume values from the stack and push results back onto it:

! Push numbers onto the stack
2 3 +    ! Results in 5 on the stack

! String manipulation
"Hello" " " "World!" 3append    ! Results in "Hello World!"

⁠Hello World Explained

Our Factor program is remarkably simple:

USE: io

"Hello World!" print

• USE: io - Imports the input/output vocabulary
• "Hello World!" - Pushes the string literal onto the stack
• print - Pops the string from the stack and prints it to stdout

⁠Key Features

⁠Quotations

Factor's most distinctive feature is quotations - blocks of code that can be treated as data:

[ 2 * ] map    ! Apply doubling function to each element
[ dup * ] keep ! Square a number while keeping the original

⁠Combinators

Higher-order functions that operate on quotations:

5 [ 1 + ] [ 2 * ] bi    ! Apply both functions: results in 6 and 10

⁠Vocabularies

Factor organizes code into vocabularies (similar to modules):

USING: math sequences io ;

⁠Language History

Factor was created by Slava Pestov in 2003, originally targeting the JVM. It has since evolved into a self-hosted language with its own virtual machine. The language is inspired by:

• Forth - Stack-based computation model
• Lisp - Metaprogramming and code-as-data philosophy
• Smalltalk - Object system and interactive development

⁠Further Exploration

• Try the interactive listener: factor
• Explore the rich vocabulary system
• Learn about Factor's unique approach to object-oriented programming
• Investigate the powerful metaprogramming capabilities
• Check out the GUI framework for desktop applications

Factor represents a unique approach to programming that challenges conventional thinking about language design while remaining highly practical and expressive.