II. Basic functions

DEFUN is used to define new functions. It takes three parameters, which are implicitly quoted (see below): (1) the name of the function, as an atom; (2) the formal parameter list of the function, as a list of atoms; and (3) an S-expression representing the body of the function. DEFUN defines the new function and return as its value the name of the function. (Note: some LISP systems use some other function, such as DEFQUOTE, to define functions.)

QUOTE takes a single S-expression as a parameter, and returns that S-expression, unevaluated, as its result.

The CAR of a nonempty list is the first element (S-expression) in that list.

The CDR of a nonempty list is the list with its first element removed.

The CONS of an S-expression to a list is the list with the S-expression inserted at the beginning, as a new first element. Note that the CAR of this new list is the given S-expression, while the CDR is the original list.

EQ compares two atoms for equality (identity) and returns ``true'' if the atoms are the same, NIL if they are different.

ATOM of an S-expression is ``true'' if the S-expression is an atom, and NIL otherwise.

NULL of an S-expression is ``true'' if the S-expression is the empty list (that is, NIL), and NIL otherwise.

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Copyright © 1995 by David Matuszek
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Last updated July 15, 1995