Editing PL/I (section)

===Teaching subset compilers===
In the late 1960s and early 1970s, many US and Canadian universities were establishing time-sharing services on campus and needed conversational compiler/interpreters for use in teaching science, mathematics, engineering, and computer science. [[Dartmouth College|Dartmouth]] was developing [[BASIC]], but PL/I was a popular choice, as it was concise and easy to teach. As the IBM offerings were unsuitable,<ref>{{cite web|url=http://plg.uwaterloo.ca/~holt/papers/fatal_disease.html|title=Teaching the Fatal Disease (or) Introductory Computer Programming Using PL/I|author=Richard C. Holt|date=November 5, 1972|access-date=May 30, 2010|archive-url=https://web.archive.org/web/20110415025435/http://plg.uwaterloo.ca/~holt/papers/fatal_disease.html|archive-date=April 15, 2011|url-status=live}}</ref> a number of schools built their own subsets of PL/I and their own interactive support. Examples are:

In the 1960s and early 1970s, [[Allen-Babcock]] implemented the Remote Users of Shared Hardware (RUSH) time sharing system for an [[IBM System/360 Model 50]] with custom [[microcode]] and subsequently implemented IBM's '''[[Conversational Programming System|CPS]]''', an interactive time-sharing system for [[OS/360]] aimed at teaching computer science basics, offered a limited subset of the PL/I language in addition to BASIC and a remote job entry facility.

'''[[PL/C]]''', a dialect for teaching, a compiler developed at [[Cornell University]], had the unusual capability of never failing to compile any program through the use of extensive automatic correction of many syntax errors and by converting any remaining syntax errors to output statements. The language was almost all of PL/I as implemented by IBM.<ref>Department of Computer Science, ''User's Guide to PL/C - The Cornell Compiler for PL/I,'' Cornell University, Ithaca, 1977.</ref> PL/C was a very fast compiler.

'''{{visible anchor|SL/1}}''' (Student Language/1, Student Language/One or Subset Language/1)<ref>{{cite web
 |url=http://teampli.net/plifamily.html#sli
 |title=SL/1 (Student Language/One)}}</ref><ref>{{cite web 
|url=http://www.bobspixels.com/kaibab.org/bob/ibm1130.htm 
|title=The IBM 1130 |website=BobsPixels.com}}</ref> was a PL/I subset, initially available late 1960s, that ran interpretively on the [[IBM 1130]]; instructional use was its strong point.

'''PLAGO''', created at the [[Polytechnic Institute of Brooklyn]], used a simplified subset of the PL/I language<ref>''PLAGO/360 User's Manual,'' Polytechnic Institute of Brooklyn.</ref> and focused on good diagnostic error messages and fast compilation times.

The Computer Systems Research Group of the University of Toronto produced the '''[[SP/k]]''' compilers which supported a sequence of subsets of PL/I called SP/1, SP/2, SP/3, ..., SP/8 for teaching programming. Programs that ran without errors under the SP/k compilers produced the same results under other contemporary PL/I compilers such as IBM's PL/I F compiler, IBM's checkout compiler or Cornell University's PL/C compiler.<ref>J. N. P. Hume and R. C. Holt, ''Structured Programming using PL/I and SP/k,'' Reston, Reston, 1975.</ref>

Other examples are '''PL0''' by P. Grouse at the University of New South Wales, '''PLUM''' by [[Marvin Victor Zelkowitz]] at the University of Maryland.,<ref>[[Marvin Victor Zelkowitz]], ''PL/I Programming with PLUM,'' 2nd Ed., Paladin House, Geneva (Ill.), 1978.</ref> and '''PLUTO''' from the University of Toronto.