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On one hand, Scheme incorporated re-invocable continuations that go beyond Actor message passing. On the other hand, Scheme did not provide for message arrival order that is part of Actors. |
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==Why an article on Scheme's history?==
This stub article was born of my work on [[Scheme (programming language)]]. As a Schemer I've been vaguely aware of much of this for some time, but as I've read that various articles on related subjects and external materials over the past few days in writing the Scheme article I've become aware that there's a lot of information scattered around but it isn't reflected anywhere on Wikipedia.
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It seems very strange. On one hand, Scheme incorporated re-invocable continuations that go beyond Actor message passing. On the other hand, Scheme did not provide for message arrival order that is part of Actor message passing. [[Special:Contributions/68.170.176.166|68.170.176.166]] ([[User talk:68.170.176.166|talk]]) 22:44, 8 November 2009 (UTC)
: You're repeating yourself, i'm repeating myself... i still see no evidence for any "controversy", and still do not think you entirely understand the text you're quoting (as i explained above).
: If you want to opine about what you perceive as being strange about Scheme's design choices, you can do it on your user page, a blog, or similar: Wikipedia is '''[[Wikipedia:What Wikipedia is not|not]]''' for personal commentary or opinions. <span style="white-space:nowrap">—[[User:Piet Delport|Piet Delport]] <small>([[User talk:Piet Delport|talk]]) 2009-11-12 21:05</small></span>
::According to work published at the time referenced above and also including [http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TR-154.pdf Semantics of Communicating Parallel Processes] , [http://dspace.mit.edu/bitstream/handle/1721.1/6272/AIM-410.pdf?sequence=2 Viewing Control Structures as Patterns of Passing Messages] and [http://portal.acm.org/citation.cfm?id=512975&coll=portal&dl=ACM Synchronization in actor systems], the following controversies were prominent in the initial development of Scheme:
::*hairy control structure ''versus'' Actor message passing
::*EVALUATE!UNINTERRUPTEDLY ''versus'' message arrival ordering
::This is what "'''Hewitt is flaming about.'''" [Sussman and Steele 1976] But now, on the basis of no evidence, you claim that the controversy never happened.[[Special:Contributions/99.29.247.230|99.29.247.230]] ([[User talk:99.29.247.230|talk]]) 19:02, 15 November 2009 (UTC)
Both of the above were part of the general controversy caused by the Sussman and Steele thesis that Actors were merely the lambda calculus in disguise. Another instance of the controversy was whether Actor customers (continuations) are lambda expression closures. [http://repository.readscheme.org/ftp/papers/ai-lab-pubs/AIM-379.pdf Steele (1976)] in the secton "Actors ≡ Closures (mod Syntax)" disagreed with Hewitt who "expressed doubt as to whether these underlying continuations can themselves be expressed as lambda expressions." However, Actor customers cannot be expressed as lambda expressions because doing so would preclude being able to enforce the Actor requirment that a customer will process at most one return value.[[Special:Contributions/68.170.178.152|68.170.178.152]] ([[User talk:68.170.178.152|talk]]) 21:56, 6 December 2009 (UTC)
==Hewitt's version of the history was published in an article at ArXiv 0907.3330==
Hewitt's version of the history was published in [http://arxiv.org/abs/0907.3330 ActorScript<sup>TM</sup>: Industrial strength integration of local and nonlocal concurrency for Client-cloud Computing] arXiv:0907.3330 [[Special:Contributions/98.210.236.39|98.210.236.39]] ([[User talk:98.210.236.39|talk]]) 11:09, 27 February 2010 (UTC)
==Carl Hewitt, the Actor model, and the birth of Scheme (added material)==
In 1971 Sussman, [[Drew McDermott]], and [[Eugene Charniak]] had developed a system called [[Planner_programming_language#Micro-planner_implementation|Micro-Planner]] which was a partial and somewhat unsatisfactory implementation of Planner. Sussman and Hewitt worked together along with others on [[MDL (programming language)|Muddle (later MDL)]], an extended Lisp which formed a component of Hewitt's ambitious [[Planner (programming language)|Planner]] project. Drew McDermott, and Sussman in 1972 developed the Lisp-based language Conniver, which revised the use of automatic backtracking in Planner which they thought was unproductive. Hewitt was dubious that the "hairy control structure" in Conniver was a solution to the the problems with Planner. Pat Hayes remarked: "Their [Sussman and McDermott] solution, to give the user access to the implementation primitives of Planner, is however, something of a retrograde step (what are Conniver's semantics?)"<ref>Pat Hayes Some Problems and Non-Problems in Representation Theory AISB’74.</ref>
In November 1972, Hewitt and his students invented the [[Actor model]] of computation as a solution to the problems with Planner.<ref name="hewitt1973">{{cite paper|author=Carl Hewitt|coauthors=Peter Bishop and Richard Steiger|title=A Universal Modular Actor Formalism for Artificial Intelligence|publisher=IJCAI|year=1973}}</ref> A partial implementation of Actors was developed called Planner-73 (later called PLASMA). Steele, then a graduate student at MIT, had been following these developments, and he and Sussman decided to implement a version of the Actor model in their own "tiny Lisp" developed on top of [[MacLisp]], in order to understand the model better. Using this basis they then began to develop mechanisms for creating actors and sending messages.<ref name="revisited">{{cite journal
| author = [[Gerald Jay Sussman]] and [[Guy L. Steele, Jr.]]
| month = December
| year = 1998
| url = http://www.brics.dk/~hosc/local/HOSC-11-4-pp399-404.pdf
| format = PDF
| title = The First Report on Scheme Revisited
| journal = Higher-Order and Symbolic Computation
| volume = 11
| issue = 4
| pages = 399–404
| doi = 10.1023/A:1010079421970
| issn = 1388-3690
| accessdate = 2006-06-19
}}</ref>
PLASMA's use of lexical scope was similar to the lambda calculus. Sussman and Steele decided to try to model Actors in the lambda calculus. They called their modeling system Schemer, eventually changing it to Scheme to fit the six-character limit on the ITS file system on their DEC PDP-10. They soon concluded Actors were essentially closures that never return but instead invoke a [[continuation]], and thus they decided that the closure and the Actor were, for the purposes of their investigation, essentially identical concepts. They eliminated what they regarded as redundant code and, at that point, discovered that they had written a very small and capable dialect of Lisp. Hewitt remained critical of the "hairy control structure" in Scheme.<ref>Carl Hewitt. "Viewing Control Structures as Patterns of Passing Messages" AI Memo 410. December 1976. Journal of Artificial Intelligence. June 1977.</ref> and considered primitives (e.g., START!PROCESS, STOP!PROCESS and EVALUATE!UNINTERRUPTIBLEY) used in the Scheme implementation to be a backward step.
25 years later, in 1998, Sussman and Steele reflected that the minimalism of Scheme was not a conscious design goal, but rather the unintended outcome of the design process. "We were actually trying to build something complicated and discovered, serendipitously, that we had accidentally designed something that met all our goals but was much simpler than we had intended....we realized that the lambda calculus—a small, simple formalism—could serve as the core of a powerful and expressive programming language." <ref name="revisited"/>
On the other hand, Hewitt remained critical of the lambda calculus as a foundation for computation writing "The actual situation is that the λ-calculus is capable of expressing some kinds of sequential and parallel control structures but, in general, not the concurrency expressed in the Actor model. On the other hand, the Actor model is capable of expressing everything in the λ-calculus and more." He has also been critical of aspects of Scheme that derive from the lambda calculus such as reliance on continuation functions and the lack of exceptions.<ref>Carl Hewitt [http://arxiv.org/abs/0907.3330 ActorScriptTM: Industrial strength integration of local and nonlocal concurrency for Client-cloud Computing] ArXiv 0907.3330</ref>
{{reflist}}
== First implementations ==
Who wrote the first implementations and how were they written? I presume they were written in MacLisp on a PDP-10 at MIT, but hope someone who has read the LAMBDA papers could share. --[[Special:Contributions/132.198.101.61|132.198.101.61]] ([[User talk:132.198.101.61|talk]]) 18:36, 13 August 2010 (UTC)
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