;;; invariant.scm -- look for invariant expressions
 ;;;
 ;;; author :  Sandra Loosemore
 ;;; date   :  12 Mar 1993
 ;;;
 ;;;
 ;;; The function flic-invariant? returns true if the expression is
 ;;; invariant with respect to a set of local variable bindings.
 
 (define-flic-walker flic-invariant? (object local-bindings))
 
 (define (flic-invariant-list? objects local-bindings)
   (if (null objects)
       '#t
       (and (flic-invariant? (car objects) local-bindings)
 	   (flic-invariant-list? (cdr objects) local-bindings))))
 
 (define-flic-invariant? flic-lambda (object local-bindings)
   (flic-invariant? (flic-lambda-body object)
 		   (cons (flic-lambda-vars object) local-bindings)))
 
 (define-flic-invariant? flic-let (object local-bindings)
   (let* ((bindings      (flic-let-bindings object))
 	 (body          (flic-let-body object))
 	 (recursive?    (flic-let-recursive? object))
 	 (inner-stuff   (cons bindings local-bindings)))
     (and (flic-invariant-list? (map (function var-value) bindings)
 			       (if recursive? inner-stuff local-bindings))
 	 (flic-invariant? body inner-stuff))))
 
 (define-flic-invariant? flic-app (object local-bindings)
   (and (flic-invariant? (flic-app-fn object) local-bindings)
        (flic-invariant-list? (flic-app-args object) local-bindings)))
 
 (define-flic-invariant? flic-ref (object local-bindings)
   (let ((var  (flic-ref-var object)))
     (or (var-toplevel? var)
 	(flic-local-var? var local-bindings))))
 
 (define (flic-local-var? var local-bindings)
   (cond ((null? local-bindings)
 	 '#f)
 	((memq var (car local-bindings))
 	 '#t)
 	(else
 	 (flic-local-var? var (cdr local-bindings)))))
 
 (define-flic-invariant? flic-const (object local-bindings)
   (declare (ignore object local-bindings))
   '#t)
 
 (define-flic-invariant? flic-pack (object local-bindings)
   (declare (ignore object local-bindings))
   '#t)
 
 (define-flic-invariant? flic-case-block (object local-bindings)
   (flic-invariant-list? (flic-case-block-exps object) local-bindings))
 
 (define-flic-invariant? flic-return-from (object local-bindings)
   (flic-invariant? (flic-return-from-exp object) local-bindings))
 
 (define-flic-invariant? flic-and (object local-bindings)
   (flic-invariant-list? (flic-and-exps object) local-bindings))
 
 (define-flic-invariant? flic-if (object local-bindings)
   (and (flic-invariant? (flic-if-test-exp object) local-bindings)
        (flic-invariant? (flic-if-then-exp object) local-bindings)
        (flic-invariant? (flic-if-else-exp object) local-bindings)))
 
 (define-flic-invariant? flic-sel (object local-bindings)
   (flic-invariant? (flic-sel-exp object) local-bindings))
 
 (define-flic-invariant? flic-is-constructor (object local-bindings)
   (flic-invariant? (flic-is-constructor-exp object) local-bindings))
 
 (define-flic-invariant? flic-con-number (object local-bindings)
   (flic-invariant? (flic-con-number-exp object) local-bindings))
 
 (define-flic-invariant? flic-void (object local-bindings)
   (declare (ignore object local-bindings))
   '#t)