While GNU APL has, as its primary focus, adherence to the APL2 ISO 13751 standard, it is open to enhancements which do not violate compatibility with APL/2.

So, as of SVN 1847M:

 undefined

              s ← 'Mississippi'
          ≠s    
    1 1 1 0 0 0 0 0 1 0 0
          (≠s)/s
    Misp

  

Whether you are an old hand at APL, or someone just discovering the language, having the symbols in the standard layout right there on your keyboard is a great help... dedicated APL keyboards are pretty expensive, so consider these stickers that let one adapt any standard desktop or laptop keyboard!

APL keyboard sticker set on Tindie

To set up your keyboard for APL programming on Linux, see here.

For Funtoo users, simply sudo emerge dev-lang/apl :)

GNU APL is easy to build on your own Linux machine, though the steps aren't detailed on the website.

Benefits of building yourself locally:

• One can customize how many cores GNU APL has access to
• Customizing optional extensions like PNG image, SQLite, GTK support etc.
• Having the latest bugfixes

1. Obtain the latest source
   • mkdir apl-build
   • svn checkout http://svn.savannah.gnu.org/svn/apl/trunk
2. Configure using autotools
   • cd trunk
   • make clean
   • ./configure CORE_COUNT_WANTED=3 RATIONAL_NUMBERS_WANTED=yes --with-ctrld_del

   Use ./configure --help to see other options, adjust to taste

3. Build and install
   • make -j && sudo make install
4. Set up your default workspace
   • cd ~
   • mkdir -p GNUAPL/workspaces