Listener examples

You can try expressions in the interactive listener. For example, some postfix arithmetic:

2 3 + 4 * .

Hello world:

"Hello world" print

Complete examples


  • hello-world - a complete program that defines a new vocabulary with a main word

Networking and web


  • rot13 - rot13 "encryption"
  • roman - convert numbers to and from roman numerals
  • morse - convert strings to morse code and vice versa, and play morse code with OpenAL
  • base64
  • id3 - ID3 parser
  • usa-cities - parse a CSV file and extract information
  • benchmark.mandel - Mandelbrot fractal generator

C library bindings

Many of these bindings have easier to use wrappers (for example, there's no reason to use the Unix API directly, since all I/O is done with higher-level cross-platform APIs). Learn more about Factor's C library interface.


These examples are more complex than the above, and some of them were written a while ago and haven't been cleaned up to use the latest idioms. They are all runnable from the Factor UI if you have a good enough OpenGL driver -- just issue a command such as "spheres" run in the listener.

Comp sci

  • rpn - Simple reverse polish notation calculator. It implements a parser, "bytecode" instruction set, and simple stack interpreter, from scratch, without re-using parts of Factor's own implementation via reflection.
  • monads - Implements a generic protocol, some operations over monads, and a few simple instances

Running the examples

Some of these examples define a MAIN: word. This means they are runnable from the Factor listener, by issuing a command such as the following,

"hello-unicode" run

Other examples are libraries, which means that after loading them with a command like this:

USE: roman

you can then get a list of words, and in some cases, API documentation:

"roman" about

and play around:

( scratchpad ) 123 >roman .

Understanding the examples

If you see an example refer to a vocabulary in its USING: list, you can get help for that vocabulary from the Factor listener:

"math.vectors" about

The about page gives a list of words with stack effects -- clicking on a word will display documentation for the word, if any, as well as its definition (which may not exactly match the source file definition, since its printed from its in-memory representation). For many vocabularies, a "Documentation" link at the very top gives an overview article as well.

If you see an example call a word you're unfamiliar with, make sure you load all required vocabularies by copying the example's USING: line into your listener, then use the help word to get help:

\ reverse help

This even works for bits of syntax:

\ MEMO: help

Finally, all of this reference documentation is also available online at http://docs.factorcode.org.


To see more examples of Factor code, download the Factor distribution and take a look in the core/, basis/ and extra/ directories. Most of Factor is implemented in Factor (including the optimizing compiler), and there are a number of useful libraries and demos which you can look at as well, for a total of over 200 thousand lines of Factor code.

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This revision created on Wed, 27 Apr 2011 11:40:48 by PhilipWalker