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(define (make-wrapper-comparator type-test unwrap contents-comparator)
(make-comparator
type-test
(lambda (a b)
((comparator-equality-predicate contents-comparator)
(unwrap a)
(unwrap b)))
(if (comparator-ordering-predicate contents-comparator)
(lambda (a b)
((comparator-ordering-predicate contents-comparator)
(unwrap a)
(unwrap b)))
#f)
(if (comparator-hash-function contents-comparator)
(lambda (x)
((comparator-hash-function contents-comparator) x))
#f)))
(define (make-product-comparator . comparators)
(let* ((type-tests
(delete-duplicates
(map comparator-type-test-predicate comparators)
eq?))
(type-test
(lambda (val)
(every (lambda (test) (test val)) type-tests))))
(make-comparator
type-test
(lambda (a b)
(every (lambda (cmp)
((comparator-equality-predicate cmp) a b))
comparators))
(if (every comparator-ordered? comparators)
(lambda (a b)
(let loop ((cmps comparators))
(cond ((null? cmps) #f)
(((comparator-ordering-predicate (car cmps)) a b) #t)
(((comparator-equality-predicate (car cmps)) a b) (loop (cdr cmps)))
(else #f))))
#f)
(if (every comparator-hashable? comparators)
(lambda (x)
(fold bitwise-xor
0
(map (lambda (cmp)
((comparator-hash-function cmp) x))
comparators)))
#f))))
(define (%sum-comparator-for comparators a b)
(define (type-tests-for? x)
(lambda (cmp) ((comparator-type-test-predicate cmp) x)))
(let ((a-cmp (find-tail (type-tests-for? a) comparators)))
(if (and a-cmp ((comparator-type-test-predicate (car a-cmp)) b))
a-cmp
(let ((b-cmp (find-tail (type-tests-for? b) comparators)))
(if (and b-cmp ((comparator-type-test-predicate (car b-cmp)) a))
b-cmp
#f)))))
(define (make-sum-comparator . comparators)
(make-comparator
(lambda (x)
(any
(lambda (cmp)
((comparator-type-test-predicate cmp) x))
comparators))
(lambda (a b)
(let ((cmp (%sum-comparator-for comparators a b)))
(if cmp
((comparator-equality-predicate (car cmp)) a b)
#f)))
(if (every comparator-ordered? comparators)
(lambda (a b)
(let ((cmp (%sum-comparator-for comparators a b)))
(if cmp
((comparator-ordering-predicate (car cmp)) a b)
(let ((a-cmp (%sum-comparator-for comparators a a))
(b-cmp (%sum-comparator-for comparators b b)))
(>= (length a-cmp) (length b-cmp))))))
#f)
(if (every comparator-hashable? comparators)
(lambda (x)
(let ((cmp (%sum-comparator-for comparators x x)))
((comparator-hash-function (car cmp)) x)))
#f)))
(define one-comparator
(make-comparator
(lambda (x) #t)
(lambda (a b) #t)
(lambda (a b) #f)
(lambda (x) 0)))
(define zero-comparator
(make-comparator
(lambda (x) #f)
(lambda (a b) (error "can't compare" a b))
(lambda (a b) (error "can't compare" a b))
(lambda (x) (error "can't hash" x))))
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