[alankay]

This is a quite inaccurate comment. The catalysts (in 1966) for the ideas I had included Sketchpad (especially), Simula I (a few days later), the ARPAnet (under discussion), operating systems inter-process communications (especially Project Genie), the Burroughs B5000, my old biology and mathematics majors. All these are mentioned in "The Early History of Smalltalk" that I wrote for the ACM History of Programming Languages"

Actors appeared after I gave a talk at MIT about the very first Smalltalk.

There were several later ideas that were discussed at Parc but not taken up because of the whirl that was already going on. One of these was derived from McCarthy's "fluents" and "situations" (essentially a labeled states/layers idea for allowing concurrencies without race conditions -- this was done very well in David Reed's 1978 MIT thesis.

Another was not waiting for replies. This was in the original set of ideas -- via biology and OS techniques -- but never got implemented in a deep way. The hardware we had at Parc was tiny and Smalltalk was expressive enough to fit a lot into a little.

Another set of ideas that were completely missed appeared in LINDA by Gelernter. This (and the larger ideas around it) are very good ways to deal with larger scalings, etc.

[ProfHewitt]

Actors were developed to synthesize and integrate a whole bunch of things including those mentioned by Alan above.

Additional important influences in addition to SmallTalk-72 [Kay November 1972] were Petri nets, Planner [Hewitt 1969], capability systems [Dennis and van Horn], semaphores [Dijkstra], the lambda calculus, and Scott-Strachey semantics failure to integrate everything using the lambda calculus.

1-way message passing is most important for hardware systems in which there is near certainty that a message will be delivered and there is no need to wait for an acknowledgement of receipt.

[kragen]

Thanks for correcting the record. I've read your HOPL paper but didn't remember.

[alankay]

In the HOPL paper is some discussion of the first design for Smalltalk, that I was working on when "the bet" happened and brought Smalltalk-72 to life as the answer to "the bet" (it used a combination of Lisp and Meta II techniques to win the bet). This made it quite easy to implement, and once Dan Ingalls implemented it, we started using it.

Smalltalk-71 was never implemented (and never had its design finshed, so there is less that can be claimed about it). But, germane to this discussion, I really liked Carl Hewitt's PLANNER language, and the entire approach to "pattern directed invocation" as he called it -- this was kind of a superset of the later Prolog, and likely influenced Prolog quite a bit.

The PLANNER ideas could be used as the communications part of an object oriented language, and I thought this would be powerful in general, and also could make a big difference in what children could implement in terms of "reasoning systems" (not just imperative action systems).

For Smalltalk-72 I used a much more programmatic approach (Meta II) to recognize messages (that also allowed new syntax/languages to be defined as object protocols (to win the bet) but this was not done comprehensively enough to really use what was great about PLANNER.

There were a few subsequent attempts to combine objects with reasoning, but none of them that I'm aware of were done with end-users in mind.

I thought the subsequent ACTOR work by Carl and his colleagues produced really important theoretical results and designs, most of which we couldn't pragmatically use in the personal computing and interface work on the rather small Xerox Parc personal computers.