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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