Special forms in Lisp

ABSTRACT

Special forms are those expressions in the Lisp language which do not follow normal rules for evaluation. Some such forms are necessary as primitives of the language, while others may be desirable in order to improve readability, control the evaluation environment, implement abstraction and modularity, affect the flow of control, allow extended scoping mechanisms, define functions which accept a variable number of arguments, or achieve greater efficiency. There exist several long-standing mechanisms for specifying the definition of special forms: FEXPR's, NLAMBDA's and MACRO's. In this paper, the motivations for using special forms are discussed, followed by a summary of the advantages and disadvantages of employing MACRO's, FEXPR's, and NLAMBDA's as tools for their implementation. It is asserted that MACRO's offer an adequate mechanism for specifying special form definitions and that FEXPR's do not. Evidence is given which supports the author's contention that FEXPR's interfere with the correct operation of code-analyzing programs such as the compiler. Finally, it is suggested that, in the design of future Lisp dialects, serious consideration be given to the proposition that FEXPR's should be omitted from the language altogether.

REFERENCES

• 1: John Allen, Anatomy of LISP, McGraw-Hill, Inc., New York, NY, 1978
• 2: Eugene Charniak , James R. Meehan , Christopher K. Reisbeck , Drew V. McDermott, Artificial Intelligence Programming, Lawrence Erlbaum Associates, Inc., Mahwah, NJ, 1987
• 3: Bernard Greenberg: Notes on the Programming Language Lisp, Student Information Processing Board, MIT, 1978.
• 4: John McCarthy, LISP 1.5 Programmer's Manual, The MIT Press, 1962
• 5: David A. Moon: Maclisp Reference Manual, Laboratory for Computer Science, MIT, March 1974.
• 6: Guy L. Steele, Jr., Rabbit: A Compiler for Scheme, Massachusetts Institute of Technology, Cambridge, MA, 1978
• 7: Guy L. Steele, Jr. and Gerald J. Sussman: The Revised Report on SCHEME, A Dialect of Lisp, AI Memo 452, Artificial Intelligence Laboratory, MIT, January 1978.
• 8: Warren Teitelman: Interlisp Reference Manual, Xerox Palo Alto Research Center, October 1978.
• 9: Daniel Weinreb, Lisp machine manual, Massachusetts Institute of Technology, 1981
• 10: Jon L. White: "NIL—A Perspective", 1979 Macsyma Users' Conference Proceedings: Washington, DC; June 20-22, 1979.
• 11: P. H. Winston , B. K. Horn, LISP, Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1988

INDEX TERMS

Primary Classification:
  F. Theory of Computation
  F.3 LOGICS AND MEANINGS OF PROGRAMS
      F.3.3 Studies of Program Constructs
          Subjects: Control primitives

Additional Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.2 Language Classifications

          Nouns: LISP
      D.3.3 Language Constructs and Features
          Subjects: Procedures, functions, and subroutines

General Terms:
Languages