CGOL (pronounced "see goll") is an alternative syntax for the MACLISP programming language, featuring an extensible algebraic notation. It was created by Vaughan Pratt.

The notation of CGOL is a traditional algebraic notation (sometimes called "infix syntax"), in the style of ALGOL, rather than Lisp's traditional, uniformly-parenthesized syntax. The CGOL parser is based on Pratt's design for top-down operator precedence parsing, sometimes informally referred to as a "Pratt parser".

Semantically, CGOL is essentially just MACLISP, with some additional reader and printer support.

Syntax

Special notations are available for many commonly used MACLISP operations. For example, one can write a matrix multiply routine as:

for i in 1 to n do
  for k in 1 to n do
    (ac := 0;
     for j in 1 to n do
        ac := ac + a(i,j)*b(j,k);
     c(i,k) := ac)

CGOL has an infix . operation (referring to MACLISP's cons function) and the infix @ operation (referring to MACLISP's append function):

a.(b@c) = (a.b)@c

The preceding example corresponds to this text in native MACLISP:

(EQUAL (CONS A (APPEND B C)) (APPEND (CONS A B) C))

CGOL uses of to read and set properties:

'father' of x := 'brother' of relative of y

The preceding example corresponds to this text in native MACLISP:

(PUTPROP X (GET (GET Y RELATIVE) 'BROTHER) 'FATHER)

This illustrates how CGOL notates a function of two arguments:

\x,y; 1/sqrt(x**2 + y**2)

The preceding example corresponds to this text in native MACLISP:

(LAMBDA (X Y) (QUOTIENT 1 (SQRT (PLUS (EXPT X 2) (EXPT Y 2)))))

The syntax of CGOL is data-driven and so both modifiable and extensible.

References

• Pratt, Vaughan R. CGOL: An Alternative External Representation for LISP Users. AI Working Paper 121. MIT Artificial Intelligence Laboratory (Cambridge, MA). 1976.
• V.R. Pratt. CGOL - an Algebraic Notation For MACLISP users. January 27, 1977.
• Pratt, V.R., Top Down Operator Precedence. Proceedings of the ACM Symposium on Principles of Programming Languages. 1973. pp41-51.