Answer till 4.73

ex-4_55-60.scm

@@ -33,7 +33,10 @@
         (salary ?person ?amount)
         (lisp-value > ?amount ?ben-amount)))
 (newline)
-; c. all people who are supervised by someone who is not in the computer ; division, together with the supervisor's name and job.  (eval-query
+
+; c. all people who are supervised by someone who is not in the computer ;
+; division, together with the supervisor's name and job.
+(eval-query
   '(and (supervisor ?person ?supervisor)
         (not (job ?supervisor (computer . ?supervisor-title)))
         (job ?supervisor ?job)))

ex-4_61-69.scm

@@ -147,5 +147,3 @@
 (eval-query '(greats (great grandson) Adam ?ggs))
 (newline)
 
-(display "\nex-4.70\n")
-

ex-4_70-79.scm

@@ -9,16 +9,44 @@
 ; itself and we would get an endless stream of the current assertion.
 (display "[answered]\n")
 
-(display "\nex-4.71\n")
+(display "\nex-4.71 - simpler-simple-query\n")
 
-; ... continue with 4.4.4.6
+; Using delay for the rule part can help to print at least some results before
+; a potential endless loop.
 
-(display "\nex-4.72\n")
+; (eval-query '(rule (married ?x ?y)
+;                    (married ?y ?x)))
+
+; (eval-query '(married Minnie ?x))
+
+(display "[answered]\n")
+
+; I got this solution from SICP solutions because I could not think of a good
+; example. It would be better to implement the loop-avoidance algorithm than
+; relying on delayed evaluation to get some results, in my opinion.
+
+(display "\nex-4.72 - stream-interleave\n")
+
+; If only one of the disjuncts produces a result and the others create an
+; endless-loop, interleaving guarantess that we get some results for the valid
+; disjuncts.
+
+(display "[answered]\n")
+
+
+(display "\nex-4.73 - explicit-delay\n")
+
+; The second argument to interleave must be delayed explicitly because
+; MIT-Scheme's applicative-order-evaluation would evaluate the complete stream,
+; otherwise. That would make the use of streams pointless.
+
+(display "[answered]\n")
+
+(display "\nex-4.74\n")
 
-;(display "\nex-4.73\n")
-;(display "\nex-4.74\n")
 ;(display "\nex-4.75\n")
 ;(display "\nex-4.76\n")
 ;(display "\nex-4.77\n")
 ;(display "\nex-4.78\n")
 ;(display "\nex-4.79\n")
+

misc/sicp-query.scm

@@ -677,6 +677,8 @@
 (son Ada Jabal)
 (son Ada Jubal)
 
+(married Mickey Minnie)
+
 ))
 
 ;; felixm: for easier use from MIT-Scheme