#| -*-Scheme-*-

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This file is part of MIT/GNU Scheme.

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|#

;;;; Operator Analysis

(declare (usual-integrations))

(define (operator-analysis procedures applications)
  (for-each (lambda (application)
	      (if (eq? (application-type application) 'COMBINATION)
		  (analyze/combination application)))
	    applications)
  (for-each (lambda (procedure)
	      (if (procedure-continuation? procedure)
		  (set-continuation/passed-out?!
		   procedure
		   (continuation-passed-out? procedure))))
	    procedures)
  (for-each (lambda (procedure)
	      (set-procedure-always-known-operator?!
	       procedure
	       (if (procedure-continuation? procedure)
		   (analyze/continuation procedure)
		   (analyze/procedure procedure))))
	    procedures))

(define (analyze/combination combination)
  (for-each (lambda (continuation)
	      (set-continuation/combinations!
	       continuation
	       (cons combination
		     (continuation/combinations continuation))))
	    (rvalue-values (combination/continuation combination))))

(define (continuation-passed-out? continuation)
  (any (lambda (combination)
	 (and (not (combination/simple-inline? combination))
	      (let ((operator (combination/operator combination)))
		(or (rvalue-passed-in? operator)
		    (any (lambda (rvalue) (not (rvalue/procedure? rvalue)))
			 (rvalue-values operator))))))
       (continuation/combinations continuation)))

(define (analyze/continuation continuation)
  (let ((returns (continuation/returns continuation))
	(combinations (continuation/combinations continuation)))
    (and (or (not (null? returns))
	     (not (null? combinations)))
	 (3-logic/and
	  (and (not (continuation/passed-out? continuation)) 'ALWAYS)
	  (3-logic/and
	   (for-some? returns
	     (lambda (return)
	       (eq? (rvalue-known-value (return/operator return))
		    continuation)))
	   (for-some? combinations
	     (lambda (combination)
	       (eq? (rvalue-known-value (combination/continuation combination))
		    continuation))))))))

(define (for-some? items predicate)
  (let loop ((items items) (default false))
    (cond ((null? items) 'ALWAYS)
	  ((predicate (car items)) (loop (cdr items) 'SOMETIMES))
	  (else default))))

(define (3-logic/and x y)
  (cond ((and (eq? x 'ALWAYS) (eq? y 'ALWAYS)) 'ALWAYS)
	((and (not x) (not y)) false)
	(else 'SOMETIMES)))

(define (analyze/procedure procedure)
  (and (not (procedure-passed-out? procedure))
       (let ((combinations (procedure-applications procedure)))
	 (and (not (null? combinations))
	      (every (lambda (combination)
		       (eq? (rvalue-known-value
			     (combination/operator combination))
			    procedure))
		     combinations)))))