Editing PL/C (section)

== Variants ==
Within the computer science department at Cornell there was a sense of pride about PL/C being associated with the university, and there were several variants of PL/C worked on by Conway, other faculty members, and graduate students.<ref name="OHCS-Gries">{{cite interview |last=Gries |first=David |subject-link= |interviewer=Robert L. Constable |title=A Conversation with David Gries |work=An Oral History of Computer Science |date=July 21, 2015 |publisher= Cornell University Library |location= |url=https://ecommons.cornell.edu/handle/1813/40576 }} See segment at 28:30.</ref>

In 1974, the PL/CT variant of PL/C, for use on interactive terminals rather than in batch job submissions, was first made available at Cornell.<ref name="acm-plct"/>  A second release was made in 1975,<ref name="plct">{{cite report |author-last=Moore | author-first=Charles G. III | author2-last=Worona | author2-first=Steven L. | author3-last=Conway | author3-first=Richard W. |date=September 1975 |title=PL/CT – A Terminal Version of PL/C – Release 2 |url=https://ecommons.cornell.edu/handle/1813/7114 |publisher=Cornell University |page= |docket=TR75-259 }}</ref> and then it was made available to outside institutions in 1976.<ref name="cw-mar76"/>  PL/CT primarily ran on an [[IBM System/370]] under [[VM/CMS]];<ref name="plct"/> it could also run in the [[IBM TSO]] environment.<ref name="acm-plct"/>  Somewhat unusually, PL/CT was not interpreted but rather was still implemented as a compiler.<ref name="acm-plct">{{cite conference | author-first=Richard | author-last=Conway | author2-first=Charles | author2-last=Moore | author3-first= Steven | author3-last=Worona | year= 1977 | contribution= An interactive version of the PL/C compiler | title= Proceedings of the 1977 annual conference (ACM '77) | publisher= Association for Computing Machinery | pages=308–314 | doi=10.1145/800179.810220 | hdl=1813/7028 | isbn=978-1-4503-2308-6 | hdl-access=free }}</ref>  

A variant under development by 1976 was PL/CS, which was a far more restricted subset of PL/I than regular PL/C and which provided direct language support for [[Assertion (software development)|assertions]].<ref name="plcs">{{cite report |author-last2=Constable | author-first2=Robert L. | author1-last=Conway | author1-first=Richard W. |date=November 1976 |title=PL/CS – A Disciplined Subset of PL/I |url=https://ecommons.cornell.edu/handle/1813/7436 |publisher=Cornell University |page= |docket=TR76-293 }}</ref>  The subset was enough, however, that PL/CS would still be suitable for teaching introductory programming classes.<ref name="toplas-plcs"/>  It was implemented as an alternate [[lexical analysis|lexical]] and [[parser|syntactic]] analyzer that then plugged into the common PL/C code generator and runtime system.<ref name="plcs"/>  PL/CS was also used in research on the [[Semantics (computer science)|formal semantics of programming languages]].<ref name="toplas-plcs">{{cite journal | author-first=Robert L. | author-last=Constable | author2-first= James E. | author2-last=Donahue | title= A Hierarchical Approach to Formal Semantics With Application to the Definition of PL/CS | journal= ACM Transactions on Programming Languages and Systems | volume=1 | number= 1 | date=July 1979 | pages= 98–114 | doi=10.1145/357062.357069 | s2cid=7915928 }}</ref>

A different implementation of the PL/CS definition came with Professor [[Tim Teitelbaum]] and his pioneering [[Cornell Program Synthesizer]] work.<ref name="cps">{{cite journal | author-first=Tim | author-last=Teitelbaum | author2-first= Thomas | author2-last=Reps | title= The Cornell Program Synthesizer: A Syntax-Directed Programming Environment | journal= Communications of the ACM | volume=24 | number=9 | date=September 1981 | pages= 563–573 | doi=10.1145/358746.358755 | s2cid=14317073 | doi-access=free }}</ref>  This  early instance of an [[integrated development environment]] was developed in 1978 for the [[PDP-11#Models|PDP-11/60]],<ref name="OHCS-Teitelbaum">{{cite interview |last=Teitelbaum |first=Tim |subject-link= |interviewer=David Gries |title=A Conversation with Tim Teitelbaum |work=An Oral History of Computer Science  |date=September 10, 2015 |publisher= Cornell University Library |location= |url=https://ecommons.cornell.edu/handle/1813/40865 }} See segments at 10:15 and 16:18.</ref> and contained a [[structured editor]] for PL/CS along with an [[incremental compiler]] as well as an [[Interpreter (computing)|interpreter]].<ref>{{cite book | title=The Synthesizer Generator: A System for Constructing Language-Based Editors | author-first=Thomas W. | author-last=Reps | author2-first= Tim | author2-last=Teitelbaum | publisher=Springer Verlag | location=New York | year= 1989 | pages=3, 9 | isbn=9781461396239 | url=https://books.google.com/books?id=yoXkBwAAQBAJ&pg=PA9 }}</ref>  The Cornell Program Synthesizer was soon adapted for the [[Terak desktop workstation]], an early personal computer,<ref name="OHCS-Teitelbaum"/> which was based on the [[LSI-11]] processor.<ref name="siguccs-marches"/>  The Terak computer found popularity for instructional use at Cornell and at other universities, as did the PL/CS available on it.<ref name="siguccs-marches"/><ref name="cdsun-111578"/>  In addition, Cornell built a link between the Terak and their IBM 370 mainframe, that would allow batch-mode execution of programs under PL/C and the obtaining of results on printers.<ref name="cornell-history-computing"/>

There was an even more experimental dialect being worked on, starting in 1975,<ref name="popl-plcv"/> that was known as PL/CV, which supplied some language support for [[formal verification|formal proof of correctness]] and which ran as a separate verifier step.<ref name="plcs"/>  The PL/CV work was led by Professor [[Robert L. Constable]].<ref name="popl-plcv"/><ref name="OHCS-Constable"/>  PL/CV used PL/CS as part of what it did,<ref name="popl-plcv"/> and indeed Constable had participated in the creation of PL/CS,<ref name="plcs"/> especially working with Conway and David Gries on the adding of assertions.<ref name="OHCS-Constable">{{cite interview |last=Constable |first=Robert L. |subject-link= |interviewer=David Gries |title=A Conversation with Robert L. Constable |work=An Oral History of Computer Science |date=July 21, 2015 |publisher= Cornell University Library |location= |url=https://ecommons.cornell.edu/handle/1813/40560 }} See segment at 16:30.</ref> A second version, PL/CV2, was released in 1978 and was presented at the [[Symposium on Principles of Programming Languages]] in 1979.<ref name="popl-plcv">{{cite conference | author-first=Robert L. | author-last=Constable | author2-first= Scott D. | author2-last=Johnson | year=1979 | contribution= A PL/CV Precis | title= Proceedings of the 6th ACM SIGACT-SIGPLAN symposium on Principles of programming languages (POPL '79) | publisher=Association for Computing Machinery | pages= 7–20 | doi=10.1145/567752.567754 }}</ref>