Astrid Rho, rho, rho of X
Always equals 1
Rho is dimension, rho rho rank.
APL is fun!

Richard M. Stallman, 1969

GNU APL is a free interpreter for the programming language APL.

The APL interpreter is an (almost) complete implementation of ISO standard 13751 aka. Programming Language APL, Extended.

The APL interpreter has implemented: In addition, GNU APL can be scripted. For example, this GNU APL home page was produced by a CGI script written in APL (see APL demo ).

GNU APL was written and is being maintained by Jürgen Sauermann.

Downloading and Installing GNU APL

GNU APL should be available on every GNU mirror (in directory apl) and at

Simple Installation of GNU APL

The simplest (though not necessarily best) way to install GNU APL is this:
  1. Visit one of the GNU mirrors and download the tar file apl-1.9.tar.gz in directory apl.
  2. Unpack the tar file: tar xzf apl-1.9.tar.gz
  3. Change to the newly created directory: cd apl-1.9
  4. Read (and follow) the instructions in files INSTALL and README-*
  5. Caveat: GNU APL creates full releases only every 1-2 years. Therefore an interpreter downloaded from a GNU mirror is inevitably outdated and likely contains errors that were fixed already. Consider using git or SVN (see below) instead.


GNU APL supposedly compiles under CYGWIN, (see, provided that the necessary libraries are installed. A 32-bit apl.exe that should run under CYGWIN lives in the download area. Use at your own risk and see README-5-WINDOWS for further information. Building GNU APL under cygwin is the method of choice if you need some of the special purpose system functions (⎕FFT, ⎕PLOT, ⎕RE, etc) that depend on non-default libraries. Due to the proliferation of Windows Versions has the support for apl.exe been discontinued. The apl.exe on the gnu mirrors was therefore creataed with an (as of today) outdated GNU APL version and will not be updated. However, building an up-to-date apl.exe should still be possible under CYGWIN. A compiled 64-bit version of GNU APL 1.8 (briefly tested under Windows 10) which was built under cygwin, but runs without cygwin being installed, is contained in file This zip file also contains an installer for an APL keyboard layout.

Subversion (SVN) and Git repositories for GNU APL

The best supported way of installing GNU APL is to check out its latest version from either its Subversion (preferred) or Git repository on Savannah. The subversion command to do that is:

svn checkout

Here is more information about using Subversion with GNU APL. Likewise, the command for a Git checkout is:

git clone

and here is more information about using Git with GNU APL.

Debian packages for GNU APL

For Debian based GNU/Linux distributions we have created source and binary packages for Debian. Look for files apl-1.9-1_amd64.deb (binary Debian package) or apl-1.9-1.debian.tar.gz (Debian source package). If you encounter a problem with these packages, then please report it, but with a solution, since the maintainer of GNU APL may use a GNU/Linux distribution with a different package manager.

GNU APL Binary

If you just want to quickly give GNU APL a try, and if you are very lucky, then you may be able to start the compiled GNU APL binary apl in the directory apl rather than installing the entire packet . The binary MAY run on a 32-bit i686 Ubuntu. Chances are, however, that it does NOT work, Please DO NOT report any problems if the binary does not run on your machine. Instead please use a better supported installation method above.

Note: The programs APxxx and APserver (support programs for shared APL variables) are not provided in binary form. Therefore you should start the apl binary with command line option --noSV. Note as well that the binary apl will not be updated with every GNU APL release. Therefore it will contain errors that have been corrected already.

Reporting Bugs

GNU APL is made up of more than 100,000 lines of C++ code. In a code of that size, programming mistakes are inevitable. Even though mistakes are hardly avoidable, they can be corrected once they are found. In order to improve the quality of GNU APL, we would like to encourage you to report errors that you find in GNU APL to .

The emails that we like the most are those that include a small example of how to reproduce the fault. You can see all previous postings to this mailing list at or subscribe to it at .


GNU APL comes with two documents: A Quick Tour of GNU APL , which was primarily written for newcomers to APL in general or to GNU APL in particular. It contains a brief introduction by examples into the APL language, followed by s short description of almost all GNU APL features.

And, for those already familiar with APL, there is a slightly more detailed info manual for GNU APL whose focus is more on the non-standard GNU APL features than on the APL language itself.

Finally, all GNU APL source code files are Doxygen documented. You can locally generate this documentation by running make DOXY in the top level directory of the GNU APL package. Or browse a (not entirely up-to-date) online version of the Doxygen documentation.

GNU APL Community

There is a growing group of people that are using GNU APL and that would like to share their APL code with other APL programmers. We have created a GNU APL Community Web page that aims at collecting and preserving links to the code provided by GNU APL users as to avoid that it gets lost.

In addition, we maintain a Bits-and-Pieces directory where we collect files that contain APL code sniplets, GNU APL workspaces, and other files that were contributed by the GNU APL Community. The Bits-and-Pieces directory is the right place for contributions for which the creation of an own hosting account would be an overkill.
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