Macros may be defined within the logic system using the form:
(defrelmacro <name> <arg-list> <body>)
which is effectively the same as a Common Lisp defmacro. Logic macros are expanded before variable translation so that logic variables may be treated as atoms. defrelmacro forms must have a fixed number of arguments. This allows different predicates with the same name but different arities to be defined. If you want to define a special form with an arbitrary number of arguments, use defrel-special-form-macro.
(defrelmacro append3 (x y z w)
(let ((iv (make-internal-var)))
`(and (append ,x ,y ,iv)
(append ,iv ,z ,w))))
==> (append3 (1) (2) (3) ?y) ?Y = (1 2 3)
KnowledgeWorks and Prolog User Guide (Macintosh version) - 01 Dec 2021 19:35:39