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The Factor programming language combines powerful language features with a full-featured library. The implementation is fully compiled for performance, while still supporting interactive development. Factor applications are portable between all common platforms. Factor can deploy stand-alone applications on all platforms. Full source code for the Factor project is available under a BSD license.

Getting Started

If you are reading this README file, you either downloaded a binary package, or checked out Factor sources from the GIT repository.

To run Factor:

  • Windows: Double-click factor.exe, or run .\ in a command prompt
  • Mac OS X: Double-click or run open in a Terminal
  • Unix: Run ./factor in a shell

A tutorial is available that can be accessed from the Factor environment:

"first-program" help

Some other simple things you can try in the listener:

"Hello, world" print

{ 4 8 15 16 23 42 } [ 2 * ] map .

1000 [1,b] sum .

4 iota  [
    "Happy Birthday " write
    2 = "dear NAME" "to You" ? print
] each


The Factor environment includes extensive reference documentation and a short "cookbook" to help you get started. The best way to read the documentation is in the UI; press F1 in the UI listener to open the help browser tool. You can also browse the documentation online.

Command Line Usage

Factor supports a number of command line switches:

Usage: factor [Factor arguments] [script] [script arguments]

Common arguments:
    -help            print this message and exit
    -i=<image>       load Factor image file <image> (default factor.image)
    -run=<vocab>     run the MAIN: entry point of <vocab>
        -run=listener    run terminal listener    run Factor development UI
    -e=<code>        evaluate <code>
    -no-user-init    suppress loading of .factor-rc

    "command-line" help
from within Factor for more information.

You can also write scripts that can be run from the terminal, by putting #!/path/to/factor at the top of your scripts and making them executable.

Source Organization

The Factor source tree is organized as follows:

  • build-support/ - scripts used for compiling Factor (not present in binary packages)
  • vm/ - Factor VM source code (not present in binary packages)
  • core/ - Factor core library
  • basis/ - Factor basis library, compiler, tools
  • extra/ - more libraries and applications
  • misc/ - editor modes, icons, etc
  • unmaintained/ - unmaintained contributions, please help!


Factor developers meet in the #concatenative channel on Drop by if you want to discuss anything related to Factor or language design in general.

Have fun!

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