Common Prolog uses a Lisp-like syntax in which variables are prefixed with "?" and normal Lisp prefix notation is used. Goals are represented as either lists or simple vectors e.g.
(reverse (1 2 3) ?x) or #(member ?x (1 2 3))
. A symbol beginning with
?
may be escaped by prefixing another
?
.i.e.
?foo
is the variable named
foo
;
??foo
is the symbol
?foo
.
The definition of append/3 from Prolog:
append([], X, X).
append([U|X], Y, [U|Z]) :-
append(X, Y, Z)
(defrel append
((append () ?x ?x))
((append (?u . ?x) ?y (?u . ?z))
(append ?x ?y ?z)))
Unlike many Lisp-based logic systems, Common Prolog uses simple vectors to represent Prolog structured terms. Thus,
functor
,
arg
, and
=..
all behave in a standard fashion:
(arg 2 (foo 3 4) (3 4))
(arg 2 #(foo 3 4) 4)
(functor (foo 3 4) \. 2)
(functor #(foo 3 4) foo 2)
(=.. #(foo 3 4) (foo 3 4))
(=.. (foo 3 4) (\. foo (3 4)))