Editing Occam (programming language) (section)

==Language revisions==
[[File:1983 Programming manual occam by INMOS Limited.jpg|thumb|1983 "occam" by INMOS Limited]]

===occam 1===
''occam 1''<ref name="oc1refman">{{cite book |author=<!--Must be person--> |author-link=Inmos |title=occam Programming Manual |publisher=Prentice-Hall |year=1984 |isbn=0-13-629296-8}}</ref> (released 1983) was a preliminary version of the language which borrowed from [[David May (computer scientist)|David May]]'s work on EPL and Tony Hoare's CSP. This supported only the VAR data type, which was an integral type corresponding to the native word length of the target architecture, and arrays of only one dimension.

===occam 2===
''occam 2''<ref name="oc2refman">{{cite book |last=Ericsson-Zenith |first=Steven |title=occam 2 Reference Manual |publisher=Prentice-Hall |year=1988 |isbn=0-13-629312-3}}</ref> is an extension produced by Inmos Ltd in 1987 that adds [[floating-point]] support, functions, multi-dimensional arrays and more data types such as varying sizes of integers (INT16, INT32) and bytes.

With this revision, occam became a language able to express useful programs, whereas occam 1 was more suited to examining algorithms and exploring the new language (however, the occam 1 compiler was written in occam 1,<ref name="cook1">{{cite conference |url=https://books.google.com/books?id=nvnnZtJWAZkC&q=architectures+languages+and+techniques+barry+cook |title= Occam on Field-Programmable Gate Arrays |last1=Cook |first1=Barry M |last2=Peel |first2=RMA |date=1999-04-11 |conference=22nd World Occam and Transputer User Group Technical Meeting |editor-last=Cook |editor-first=Barry M. |book-title=Architectures, Languages and Techniques for Concurrent Systems |publisher=IOS Press |location=Keele, United Kingdom |isbn= 90-5199-480-X |page=219 |access-date=2016-11-28}}</ref> so there is an existence proof that reasonably sized, useful programs could be written in occam 1, despite its limits).

===occam 2.1===
''occam 2.1''<ref name="oc21refman"/> was the last of the series of occam language developments contributed by Inmos. Defined in 1994, it was influenced by an earlier proposal for an '''occam 3''' language (also referred to as "occam91" during its early development) created by Geoff Barrett at Inmos in the early 1990s. A revised Reference Manual describing occam 3 was distributed for community comment,<ref name="occam3">{{cite journal |last1=Barrett |first1=Geoff |last2=Ericsson-Zenith |first2=Steven |title=occam 3 Reference Manual |url=http://www.wotug.org/occam/documentation/oc3refman.pdf |date=1992-03-31 |publisher=[[Inmos]] |access-date=2008-03-24}}</ref> but the language was never fully implemented in a compiler.

occam 2.1 introduced several new features to occam 2, including:
*Named data types (DATA TYPE x IS y)
*Named records
*Packed records
*Relaxation of some of the type conversion rules
*New operators (e.g. BYTESIN)
*Channel retyping and channel arrays
*Ability to return fixed-length array from function.

For a full list of the changes see Appendix P of the [http://www.wotug.org/occam/documentation/oc21refman.pdf Inmos occam 2.1 Reference Manual].

===occam-π===
''[[occam-π]]''<ref name="kroc">{{cite web |url=http://www.cs.kent.ac.uk/projects/ofa/kroc/ |title=occam-pi: Blending the best of CSP and the pi-calculus |last1=Barnes |first1=Fred |last2=Welch |first2=Peter |date=2006-01-14 |access-date=2006-11-24}}</ref> is the common name for the occam variant implemented by later versions of the Kent Retargetable occam Compiler ([[KRoC]]). The addition of the symbol ''[[Pi (letter)|π]]'' (pi) to the occam name is an allusion to KRoC occam including several ideas inspired by the [[π-calculus]]. It contains several significant extensions to the occam 2.1 compiler, for example:
*[[Nesting (computing)|Nested]] [[Protocol (object-oriented programming)|protocols]]
*Run-time process creation
*Mobile channels, data, and processes
*[[Recursion (computer science)|Recursion]]
*Protocol [[Inheritance (object-oriented programming)|inheritance]]
*Array [[Constructor (object-oriented programming)|constructors]]
*Extended [[Barrier (computer science)|rendezvous]]