Our data center had one LA36 DECwriter II terminal that had the special APL character set, and a small number of enthusiasts used to fight over who got to use it. The losers had to use standard DECwriter II terminals or glass TTYs (from Televideo or Perkin-Elmer) and type in the verbose equivalents of the symbols. I have no idea why we had APL on our System/370; it was never used for anything but fooling around.
APL was launched on Dec. 1, 1966, and had been invented by Kenneth Iverson, an IBM researcher. Amazingly, IBM still sells APL tools today, 40 years later, though they’re richly priced at US$1,741 for one workstation license with 12 months maintenance. Dr. Iverson passed away in Oct. 2004.
APL is an interpreted language designed for working with numerical arrays. You can perform complex calculations with only a few characters; designing algorithms to be concise (and often unreadable) is a marvelous talent. Sadly, I didn’t spend enough time with APL to develop much skill. My “real” work involved PL/1, COBOL and FORTRAN, and noodling with APL was essentially a hobby.
For a quick overview of APL, I’ll refer you to the Wikipedia (which is where the keyboard image above comes from). However, that article merely scratches the surface, and doesn’t show the beauty and elegance of APL programming.
In the early 1980s, I evaluated an APL interpreter for DOS, called APL*Plus, from STSC. It was a bizarre implementation, and unstable. Alas, I haven’t worked with the language since.