Editing APL (programming language) (section)

=== Hardware ===
[[File:APL Greek characters.jpg|thumb|IBM typeballs and typewheel containing APL Greek characters]]
[[File:APL-keybd2.svg|thumb|A programmer's view of the IBM 2741 keyboard layout with the APL typing element print head inserted]]

A key development in the ability to use APL effectively, before the wide use of [[Computer monitor#Cathode-ray tube|cathode-ray tube]] (CRT) terminals, was the development of a special [[IBM Selectric typewriter]] interchangeable typing element with all the special APL characters on it. This was used on paper printing terminal workstations using the Selectric typewriter and typing element mechanism, such as the [[IBM 1050]] and [[IBM 2741]] terminal. Keycaps could be placed over the normal keys to show which APL characters would be entered and typed when that key was struck. For the first time, a programmer could type in and see proper APL characters as used in Iverson's notation and not be forced to use awkward English keyword representations of them. Falkoff and Iverson had the special APL Selectric typing elements, 987 and 988, designed in late 1964, although no APL computer system was available to use them.<ref name="APLQQ91">Breed, Larry, [http://portal.acm.org/citation.cfm?id=138094.140933 "The First APL Terminal Session"], ''APL Quote Quad'', Association for Computing Machinery, Volume 22, Number 1, September 1991, p. 2–4.</ref> Iverson cited Falkoff as the inspiration for the idea of using an IBM Selectric typing element for the APL character set.<ref>[http://www.computerhistory.org/tdih/?setdate=December 19, 2009 Adin Falkoff] – Computer History Museum. "Iverson credited him for choosing the name APL and the introduction of the IBM golf-ball typewriter with the replacement typehead, which provided the famous character set to represent programs."</ref>

Many APL symbols, even with the APL characters on the Selectric typing element, still had to be typed in by over-striking two extant element characters. An example is the ''grade up'' character, which had to be made from a ''delta'' (shift-H) and a ''[[Sheffer stroke]]'' (shift-M). This was necessary because the APL character set was much larger than the 88 characters allowed on the typing element, even when letters were restricted to upper-case (capitals).