Hi Lodewijk:

our research paths cross once more. Doug Orleans,
one of my PhD students has a concept, called branches,
that can conveniently simulate composition filters.

Branches are briefly described at:

http://www.ccs.neu.edu/research/demeter/papers/predicate-dispatch-position/submission.txt

Do you have some other composition filter examples that
you think would challenge the capabilities of branches?

Best regards,
-- Karl

From dougo@ccs.neu.edu  Tue Nov 27 10:34:56 2001
From: Doug Orleans <dougo@ccs.neu.edu>
Date: Tue, 27 Nov 2001 10:34:53 -0500 (EST)
To: lieber@ccs.neu.edu
Subject: composition filters example

FYI, here's a sketch of how I might translate the composition filters
example from the CACM AOP issue into Fred:

;; page 54

;; Composition filters:
;; DocProt : Error =
;; { FinancialResp => {setApprovedClaim, setClaimAmount},
;;   MedicalResp => {setClientCategory, setMedicalCheckData},
;;   True ~> {setApprovedClaim, setClaimAmount, setClientCategory,
;;            setMedicalCheckData} };

(define (responsibility-of-caller dp)
  (responsibility (car (dp-args (dp-previous dp)))
(define-predicate financial-resp?
  (eq? (responsibility-of-caller dp) 'financial))
(define-predicate medical-resp?
  (eq? (responsibility-of-caller dp) 'medical))

(define-predicate disallowed-modification?
  (and (prot-claim-document? (car (dp-args dp)))
       (let ((msg (dp-msg dp)))
	 (not (or (and (financial-resp? dp)
		       (or (eq? msg set-approved-claim)
			   (eq? msg set-claim-amount)))
		  (and (medical-resp? dp)
		       (or (eq? msg set-client-category)
			   (eq? msg set-medical-check-data)))
		  (not (memq msg (list set-approved-claim
				       set-claim-amount
				       set-client-category
				       set-medical-check-data)))))))

(define-around (disallowed-modification? dp)
  (error "That modification is not allowed."))

--Doug