scheme48/scheme/env/shadow.scm

; Part of Scheme 48 1.9.  See file COPYING for notices and license.

; Authors: Richard Kelsey, Jonathan Rees, Mike Sperber


; Deal with shadowed variables.

; When a variable is shadowed by a variable, split the existing shared
; location into two replacement locations.

; name (structure-ref p name) (define name ...) within a single template
; will lose big.

;(define *replaced-locations* '()) ;alist of (old rep ((uid ...) . new))

(define (shadow-location! old p-uids new replacement)
  (if (location-defined? old)
      (set-contents! replacement (contents old)))
  (set-location-id! old
		    (vector replacement p-uids new))
  (set-location-defined?! old #f))  ;so that exceptions will be raised

(define maybe-replace-location
  (let ((memv memv))
    (lambda (loc p-uid)			;Package's unique id
      (let ((foo (location-id loc)))
	(if (vector? foo)
	    (maybe-replace-location
	     (if (memv p-uid (vector-ref foo 1))
		 (vector-ref foo 2)
		 (vector-ref foo 0))
	     p-uid)
	    loc)))))

; Exception handler:

(define (deal-with-replaced-variables succeed)
  (lambda (opcode reason loc template index . rest)
    (if (= reason (enum exception undefined-global))
	(deal-with-replaced-variable opcode reason loc template index rest
				     succeed)
	(apply signal-global-exception opcode reason loc rest))))

(define (deal-with-replaced-variable opcode reason loc template index rest
				     succeed)
  (primitive-catch
   (lambda (cont)
     (if (eq? (template-ref template index) loc)
	 (let* ((p-uid (template-package-id template))
		(new (maybe-replace-location loc p-uid)))
	   (if (eq? new loc)
	       (apply signal-global-exception opcode reason loc rest)
	       (begin (template-set! template index new)
		      ;(note 'deal-with-replaced-variable "Replaced location" loc new p-uid)
		      (if (location-defined? new)
			  (succeed new rest)
			  (apply signal-global-exception opcode reason loc new rest)))))
	 (assertion-violation 'deal-with-replaced-variable
			      "lossage in deal-with-replaced-variables"
			      loc index)))))

(define (signal-global-exception opcode reason loc . rest)
  (signal-condition
   (condition
    (construct-vm-exception opcode reason)
    (make-assertion-violation)
    (make-who-condition (enumerand->name opcode op))
    (make-message-condition
     (if (location-defined? loc)
	 "unassigned variable"
	 "undefined variable"))
    (make-irritants-condition
     (cons (or (location-name loc) loc)
	   (let ((pack (location-package-name loc)))
	     (if pack
		 (cons pack rest)
		 rest)))))))

(define-vm-exception-handler (enum op global)
  (deal-with-replaced-variables
   (lambda (loc more-args)
     (contents loc))))

(define-vm-exception-handler (enum op set-global!)
  (deal-with-replaced-variables
   (lambda (loc more-args)
     (set-contents! loc (car more-args)))))