Function: BUILD-COMPARATOR

Source

(defun build-comparator (eql &key < >)
  (if (and (not <)
	   (not >))
      (error "needs < or > key")
      (lambda (v1 v2)
	(cond ((funcall eql v1 v2) 'equals)
	      (< (if (funcall < v1 v2)
		     'less-than
		     'greater-than))
	      (> (if (funcall > v1 v2)
		     'greater-than
		     'lesser-than))))))