Carl Eddie Hewitt (; 1944 – 7 December 2022)''Carl Hewitt''
Stanford. 2022. was an American computer scientist who designed the Planner programming language for

automated planning Automated planning and scheduling, sometimes denoted as simply AI planning, is a branch of artificial intelligence that concerns the realization of strategy, strategies or action sequences, typically for execution by intelligent agents, autonomou ...

Carl Hewitt
''PLANNER: A Language for Proving Theorems in Robots''
IJCAI. 1969. and the

actor model The actor model in computer science is a mathematical model of concurrent computation that treats an ''actor'' as the basic building block of concurrent computation. In response to a message it receives, an actor can: make local decisions, create ...

of concurrent computation, which have been influential in the development of

logic Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the study of deductively valid inferences or logical truths. It examines how conclusions follow from premises based on the structure o ...

, functional and

object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of '' objects''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impl ...

. Planner was the first

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

based on procedural plans invoked using pattern-directed invocation from assertions and goals. The actor model influenced the development of the Scheme programming language, the

π-calculus In theoretical computer science, the -calculus (or pi-calculus) is a process calculus. The -calculus allows channel names to be communicated along the channels themselves, and in this matter, it is able to describe concurrent computations whose ...

, and served as an inspiration for several other programming languages.

Education and career

Hewitt obtained his PhD in mathematics at MIT in 1971, under the supervision of Seymour Papert, Marvin Minsky, and Mike Paterson. He began his employment at MIT that year, and retired from the faculty of the MIT Department of Electrical Engineering and Computer Science during the 1999–2000 school year. He became emeritus in the department in 2000. Among the doctoral students that Hewitt supervised during his time at MIT are Gul Agha, Henry Baker, William Clinger, Irene Greif, and Akinori Yonezawa. From September 1989 to August 1990, Hewitt was the IBM Chair Visiting Professor in the Department of Computer Science at Keio University in Japan. He has also been a visiting professor at

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...

Research

Hewitt was best known for his work on the

of computation. For the last decade, his work had been in "inconsistency robustness", which aims to provide practical rigorous foundations for systems dealing with pervasively inconsistent information. This work grew out of his doctoral dissertation focused on the procedural (as opposed to logical) embedding of knowledge, which was embodied in the Planner programming language. His publications also include contributions in the areas of open information systems, organizational and multi-agent systems,

logic programming Logic programming is a programming, database and knowledge representation paradigm based on formal logic. A logic program is a set of sentences in logical form, representing knowledge about some problem domain. Computation is performed by applyin ...

, concurrent programming,

paraconsistent logic Paraconsistent logic is a type of non-classical logic that allows for the coexistence of contradictory statements without leading to a logical explosion where anything can be proven true. Specifically, paraconsistent logic is the subfield of log ...

and

cloud computing Cloud computing is "a paradigm for enabling network access to a scalable and elastic pool of shareable physical or virtual resources with self-service provisioning and administration on-demand," according to International Organization for ...

Planner

The Planner language was developed during the late 1960s as part of Hewitt's doctoral research in MIT's Artificial Intelligence Laboratory. Hewitt's work on Planner introduced the notion of the "procedural embedding of knowledge", which was an alternative to the logical approach to knowledge encoding for

artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...

pioneered by John McCarthy. Planner has been described as "extremely ambitious". A subset of Planner called Micro-Planner was implemented at MIT by Gerry Sussman, Drew McDermott, Eugene Charniak and Terry WinogradGerry Sussman and Terry Winograd.
Micro-planner Reference Manual
' AI Memo No, 203, MIT Project MAC, July 1970. and was used in Winograd's

SHRDLU SHRDLU is an early natural-language understanding computer program that was developed by Terry Winograd at MIT in 1968–1970. In the program, the user carries on a conversation with the computer, moving objects, naming collections and query ...

program,Terry Winograd.
Procedures as a Representation for Data in a Computer Program for Understanding Natural Language
' MIT AI TR-235. January 1971. Charniak's natural language story understanding work,Marvin Minsky and Seymour Papert. "Progress Report on Artificial Intelligence" MIT AI Memo 252. 1971. and L. Thorne McCarty's work on legal reasoning. Planner was almost completely implemented in PoplerJulian Davies. Popler 1.6 Reference Manual University of Edinburgh, TPU Report No. 1, May 1973. by Julian Davies at Edinburgh. Planner also influenced the later development of other AI research languages such as Muddle and Conniver, as well as the

Smalltalk Smalltalk is a purely object oriented programming language (OOP) that was originally created in the 1970s for educational use, specifically for constructionist learning, but later found use in business. It was created at Xerox PARC by Learni ...

object-oriented programming language. Hewitt's own work on Planner continued with Muddle (later called MDL), which was developed in the early 1970s by Sussman, Hewitt, Chris Reeve, and David Cressey as a stepping-stone towards a full implementation of Planner. Muddle was implemented as an extended version of

Lisp Lisp (historically LISP, an abbreviation of "list processing") is a family of programming languages with a long history and a distinctive, fully parenthesized Polish notation#Explanation, prefix notation. Originally specified in the late 1950s, ...

, and introduced several features that were later adopted by Conniver, Lisp Machine Lisp, and Common Lisp. However, in late 1972 Hewitt abruptly halted his development of the Planner design in his thesis, when he and his graduate students invented the

of computation.

Actor model

Hewitt's work on the

of computation spanned over 30 years, beginning with the introduction of the model in a 1973 paper authored by Hewitt, Peter Bishop, and Richard Steiger, and including new results on actor model semantics published as recently as 2006.Carl Hewit
''What is Commitment? Physical, Organizational, and Social''
COIN@AAMAS. April 27, 2006. Much of this work was carried out in collaboration with students in Hewitt's Message Passing Semantics Group at MIT's Artificial Intelligence Lab. Sussman and Steele developed the Scheme programming language in an effort to gain a better understanding of the actor model. They discovered that their operator to create an actor, ALPHA, and their operator to create a function, LAMBDA, were identical, so they only kept LAMBDA for both. A number of other programming languages were developed to specifically implement the actor model, such as ACT-1, SALSA, Caltrop, E and ActorScript. The actor model also influenced the development of the

.Robin Milner Elements of interaction: Turing award lecture CACM. January 1993. (See actor model and process calculi history.)

Selected works

* Carl Hewitt (1969)
''PLANNER: A Language for Proving Theorems in Robots''
IJCAI'69. * Carl Hewitt, Peter Bishop and Richard Steiger (1973)
''A Universal Modular Actor Formalism for Artificial Intelligence''
IJCAI'73. * Carl Hewitt and Henry Baker (1977a). ''Laws for Communicating Parallel Processes'' IFIP'77. * Carl Hewitt and Henry Baker (1977b)
''Actors and Continuous Functionals''
Proceeding of IFIP Working Conference on Formal Description of Programming Concepts. August 1–5, 1977. * William Kornfeld and Carl Hewitt (1981)
''The Scientific Community Metaphor''
IEEE Transactions on Systems, Man, and Cybernetics. January 1981. * Henry Lieberman and Carl E. Hewitt (1983)

Communications of the ACM, 26(6). * Carl Hewitt (1985). ''The Challenge of Open Systems'' Byte Magazine. April 1985. (Reprinted in ''The foundation of artificial intelligence—a sourcebook'' Cambridge University Press. 1990

References

External links

* *
Hewitt's official blog
{{DEFAULTSORT:Hewitt, Carl 2022 deaths American computer programmers American computer scientists 20th-century American mathematicians 21st-century American mathematicians Formal methods people MIT School of Engineering faculty Academic staff of Keio University American technology writers Engineers from Massachusetts 1944 births