; Metalinguistic Abstraction with Hal
; Implementing a declarative/logical programming language.

;;; EXAMPLE in imperative form:
;(define (merge x y)
;  (cond
;   ((null? x) y)
;   ((null? y) x)
;   (else
;    (let ((a (car x)) (b (car y)))
;      (if (< a b)
;          (cons a
;                (merge (cdr x) y))
;          (cons b
;                (merge x (cdr y))))))))

; 8A:(18m25s)
; QUESTION, BREAK


; 8A:(21m20s) "Making a collection of facts"
;; Ben Bitdiddle (underpaid computer wizard)
;(job (Bitdiddle Ben) (computer wizard))
;(salary (Bitdiddle Ben) 40000)
;(supervisor (Bitdiddle Ben)
;            (Warbucks Oliver))
;(address (Bitdiddle Ben)
;         (Slunerville (Ridge Road) 10))
;; Alyssa P. Hacker
;(address (Hacker Alyssa P)
;         (Cambridge (Mass Ave) 78)
;(job (Hacker Alyssa P)
;     (computer programmer))
;(salary (Hacker Alyssa P) 35000)
;(supervisor (Hacker Alyssa P)
;            (Bitdiddle Ben))
;; Lem E. Tweakit
;(address (Tweakit Lem E)
;         (Boston (Bay State Road) 22))
;(job (Tweakit Len E)
;     (computer technician))
;(salary (Tweakit Len E) 15000)
;(supervisor (Tweakit Lem E)
;            (Bitdiddle Ben))
;; Louis Reasoner
;(address (Reasoner Louis)
;         (Slunerville (Pine Tree Road)
;                      80))
;(job (Reasoner Louis)
;     (computer programmer trainee))
;(salary (Reasoner Louis) 20000)
;(supervisor (Reasoner Louis)
;            (Hacker Alyssa P))
;; Oliver Warbucks
;(job (Warbucks Oliver)
;     (administration big wheel))
;(salary (Warbucks Oliver) 100000)
;(address (Warbucks Oliver)
;         (Swellesley (The Manor)))

; "Now, fine... What are the primitives?
;  What are the Means of Combination?
;  And what are the Means of Abstraction?"

;(job ?x (computer ?type))
;; MATCHES
;(job (Bitdiddle Ben) (computer wizard))
;(job (Hacker Alyssa P)
;     (computer programmer))
;(job (Tweakit Lem E)
;     (computer technician))
;; DOESN'T MATCH
;(job (Reasoner Louis)
;     (computer programmer trainee))

;(job ?x (computer . ?type))
;; WOULD (because of the Lisp reader) ALSO MATCH:
;(job (Reasoner Louis)
;     (computer programmer trainee))

; ONE PRIMITIVE: QUERY
; MEANS OF COMBINATION:
;   LISP-VALUE
;   AND
;   NOT
;   OR
; MEANS OF ABSTRACTION: RULE

; 8A:(34m50s)
;;; EXAMPLE in logical form:
;(rule (merge-to-form () ?y ?y))
;(rule (merge-to-form ?y () ?y))
;(rule
; (merge-to-form
;  (?a . ?x) (?b . ?y) (?b . ?z))
; (and (merge-to-form (?a . ?x) ?y ?z)
;      (lisp-value > ?a ?b)))
;(rule
; (merge-to-form
;  (?a . ?x) (?b . ?y) (?a . ?z))
; (and (merge-to-form ?x (?b . ?y) ?z)
;      (lisp-value > ?b ?a)))

; QUESTION 8A:(40m) (END)