Chapter 4, Metalinguistic Abstraction
Exercise 4.43
Here is my solution:
I believe that unless something is directly given in the question, we should not deduce anything, i.e. deductions should be left for the code.
(Used nested lets as in previous exercise to narrow down the possibilities)
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(define (yacht-puzzle)
(let ((lorna-yacht-owner 'moore)
(gabrielle-yacht-owner 'barnacle)
(rosalind-yacht-owner 'hall)
(melissa-yacht-owner 'downing)
(melissa-father 'barnacle)
(mary-father 'moore)
(mary-yacht-owner (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list lorna-yacht-owner
gabrielle-yacht-owner
rosalind-yacht-owner
melissa-yacht-owner
mary-yacht-owner)))
(require (not (eq? mary-yacht-owner mary-father)))
(let ((gabrielle-father (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list melissa-father mary-father gabrielle-father)))
(require (not (eq? gabrielle-father gabrielle-yacht-owner)))
(let ((rosalind-father (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list melissa-father mary-father gabrielle-father rosalind-father)))
(require (not (eq? rosalind-father rosalind-yacht-owner)))
(let ((lorna-father (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list melissa-father mary-father gabrielle-father rosalind-father lorna-father)))
(require (not (eq? lorna-father lorna-yacht-owner)))
(let ((lorna (cons lorna-father lorna-yacht-owner))
(gabrielle (cons gabrielle-father gabrielle-yacht-owner))
(rosalind (cons rosalind-father rosalind-yacht-owner))
(melissa (cons melissa-father melissa-yacht-owner))
(mary (cons mary-father mary-yacht-owner)))
(define (father daughter-name)
(car daughter-name))
(define (yacht-owner daughter-name)
(cdr daughter-name))
(let ((parker-daughter (amb lorna gabrielle rosalind melissa mary)))
(require (eq? (father parker-daughter) 'parker))
(require (eq? gabrielle-father (yacht-owner parker-daughter)))
(list
(list 'lorna-father lorna-father 'lorna-yach-owner lorna-yacht-owner)
(list 'gabrielle-father gabrielle-father 'gabrielle-yacht-owner gabrielle-yacht-owner)
(list 'rosalind-father rosalind-father 'rosalind-yacht-owner rosalind-yacht-owner)
(list 'melissa-father melissa-father 'melissa-yacht-owner melissa-yacht-owner)
(list 'mary-father mary-father 'mary-yacht-owner mary-yacht-owner)))))))))
This gives us answer:
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;;; Amb-Eval value:
((lorna-father downing lorna-yach-owner moore) (gabrielle-father hall gabrielle-yacht-owner barnacle) (rosalind-father parker rosalind-yacht-owner hall) (melissa-father barnacle melissa-yacht-owner downing) (mary-father moore mary-yacht-owner parker))
Change in mary’s father
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(define (yacht-puzzle)
(let ((lorna-yacht-owner 'moore)
(gabrielle-yacht-owner 'barnacle)
(rosalind-yacht-owner 'hall)
(melissa-yacht-owner 'downing)
(melissa-father 'barnacle)
(mary-father (amb 'moore 'downing 'hall 'barnacle 'parker)) ;;changed
(mary-yacht-owner (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list lorna-yacht-owner
gabrielle-yacht-owner
rosalind-yacht-owner
melissa-yacht-owner
mary-yacht-owner)))
(require (distinct? (list melissa-father mary-father))) ;;changed
(require (not (eq? mary-yacht-owner mary-father)))
(let ((gabrielle-father (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list melissa-father mary-father gabrielle-father)))
(require (not (eq? gabrielle-father gabrielle-yacht-owner)))
(let ((rosalind-father (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list melissa-father mary-father gabrielle-father rosalind-father)))
(require (not (eq? rosalind-father rosalind-yacht-owner)))
(let ((lorna-father (amb 'moore 'downing 'hall 'barnacle 'parker)))
(require (distinct? (list melissa-father mary-father gabrielle-father rosalind-father lorna-father)))
(require (not (eq? lorna-father lorna-yacht-owner)))
(let ((lorna (cons lorna-father lorna-yacht-owner))
(gabrielle (cons gabrielle-father gabrielle-yacht-owner))
(rosalind (cons rosalind-father rosalind-yacht-owner))
(melissa (cons melissa-father melissa-yacht-owner))
(mary (cons mary-father mary-yacht-owner)))
(define (father daughter)
(car daughter))
(define (yacht-owner daughter)
(cdr daughter))
(let ((parker-daughter (amb lorna gabrielle rosalind melissa mary)))
(require (eq? (father parker-daughter) 'parker))
(require (eq? gabrielle-father (yacht-owner parker-daughter)))
(list
(list 'lorna-father lorna-father 'lorna-yach-owner lorna-yacht-owner)
(list 'gabrielle-father gabrielle-father 'gabrielle-yacht-owner gabrielle-yacht-owner)
(list 'rosalind-father rosalind-father 'rosalind-yacht-owner rosalind-yacht-owner)
(list 'melissa-father melissa-father 'melissa-yacht-owner melissa-yacht-owner)
(list 'mary-father mary-father 'mary-yacht-owner mary-yacht-owner)))))))))
Output:
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;;; Amb-Eval value:
((lorna-father downing lorna-yach-owner moore) (gabrielle-father hall gabrielle-yacht-owner barnacle) (rosalind-father parker rosalind-yacht-owner hall) (melissa-father barnacle melissa-yacht-owner downing) (mary-father moore mary-yacht-owner parker))
;;; Amb-Eval input:
try-again
;;; Amb-Eval value:
((lorna-father parker lorna-yach-owner moore) (gabrielle-father moore gabrielle-yacht-owner barnacle) (rosalind-father downing rosalind-yacht-owner hall) (melissa-father barnacle melissa-yacht-owner downing) (mary-father hall mary-yacht-owner parker))
Here we get 2 possible answers.