Macro

Syntax

with-rule-actions bound-variables &body body

Arguments

bound-variables is a list of variables (each starting with ? ) which are already bound. body is a rule body consisting of the same kind of statements that make up the right hand side of a forward or backward chaining rule.

Description

This macro enables rule syntax to be embedded within Lisp. The body is executed just as if it were the right hand side of a rule. All variables in the body (denoted by ? ) are taken to be unbound unless found in the list bound-variables in which case its value is taken from the Lisp variable of the same name. It is similar to the function any but can be compiled for efficiency.

Values

T if the body succeeds (that is, all statements are successfully executed), else nil (if the statements fail).

Example

(defun my-fn (?x)

  "prints all the lists which append to give ?x and

   then returns NIL"

  (with-rule-actions (?x)

    (append ?a ?b ?x)

    ((format t "~%~S and ~S append to give ~S"

             ?a ?b ?x))

    (fail)))

See Also

any