CGOL - an Alternative External Representation For LISP users

Unknown author (1976-03)

This report describes research done at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology. Support for the laboratory's artificial intelligence research is provided in part by the Advanced Research Projects Agency of the Department of Defense under Office of Naval Research contract N00014-75-C-0643.

Working Paper

Advantages of the standard external representation of LISP include its simple definition, its economical implementation and its convenient extensibility. These advantages have been gained by trading off syntactic variety for the rigidity of parenthesized prefix notation. This paper describes an approach to increasing the available notational variety in LISP without compromising the above advantages of the standard notation. A primary advantage of the availability of such variety is the extent to which documentation can be incorporated into the code itself, decreasing the chance of mismatches between cods and documentation. The approach differs from that of MLISP[superscript 4], which attempts to be a self-contained language rather than a notation available immediately on demand to the ordinary LISP user. A striking feature of a MACLISP implementation of this approach, the CGOL notation, is that any LISP user, at any time, without any prior preparation, and without significant compromise of storage or speed, can in mid-stream change to the CGOL notation merely by typing (CGOL) at the LISP he is presently using, even if he has already loaded and begun running his LISP program. Another striking feature is the possibility of notational transparency; a LISP user may ask LISP to read a file without needing to know the notation(s) used within that file.