Elephant 2000: A Programming Language Based on Speech Acts

John McCarthy, Stanford University

I meant what I said, and I said what I meant. An elephant's faithful, one hundred percent!

moreover,

An elephant never forgets!

Abstract:

Elephant 2000 is a proposed programming language good for writing and verifying programs that interact with people (e.g. transaction processing) or interact with programs belonging to other organizations (e.g. electronic data interchange)

1. Communication inputs and outputs are in an I-O language whose sentences are meaningful speech acts identified in the language as questions, answers, offers, acceptances, declinations, requests, permissions and promises.
2. The correctness of programs is partly defined in terms of proper performance of the speech acts. Answers should be truthful and responsive, and promises should be kept. Sentences of logic expressing these forms of correctness can be generated automatically from the form of the program.
3. Elephant source programs may not need data structures, because they can refer directly to the past. Thus a program can say that an airline passenger has a reservation if he has made one and hasn't cancelled it.
4. Elephant programs themselves can be represented as sentences of logic. Their extensional properties follow from this representation without an intervening theory of programming or anything like Hoare axioms.
5. Elephant programs that interact non-trivially with the outside world can have both input-output specifications, relating the programs inputs and outputs, and accomplishment specifications concerning what the program accomplishes in the world. These concepts are respectively generalizations of the philosophers' illocutionary and perlocutionary speech acts.
6. Programs that engage in commercial transactions assume obligations on behalf of their owners in exchange for obligations assumed by other entities. It may be part of the specifications of an Elephant 2000 programs that these obligations are exchanged as intended, and this too can be expressed by a logical sentence.
7. Human speech acts involve intelligence. Elephant 2000 is on the borderline of AI, but the article emphasizes the Elephant usages that do not require AI.

• Introduction
• Speech Acts and Abstract Performatives
• Referring to the past
• The Structure of Elephant 2000 programs
• Examples of Programs
• Abstract Objects
• Implementation
• Specifying and Verifying Elephant 2000 Programs
• Levels of Intentionality
• Responsiveness
• Connections with Artificial Intelligence
• Domain of Application
• Algol 48 and Algol 50
  • Algol 48
  • Algol 50
• Elephant Programs as Sentences of Logic
• Remarks
• Acknowledgements
• References
• About this document ...