(module simple-goal-test mzscheme
  
  (require (planet "inference.ss" ("williams" "inference.plt")))
  
  (define-ruleset simple-goal-test-rules)
  
  (define-rule (rule-1 simple-goal-test-rules)
      (overworked ?x)
    <==
      (lecturing ?x)
      (marking-practicals ?x))
  
  (define-rule (rule-2 simple-goal-test-rules)
      (lecturing alison)
    <==
      (month february))
  
  (define-rule (rule-3 simple-goal-test-rules)
      (marking-practicals ?x)
    <==
      (month february))
  
  (define-rule (rule-4 simple-goal-test-rules)
      (bad-mood ?x)
    <==
      (overworked ?x))
  
  (define-rule (rule-5 simple-goal-test-rules)
      (bad-mood ?x)
    <==
      (slept-badly ?x))
  
  (define-rule (rule-6 simple-goal-test-rules)
      (weather cold)
    <==
      (month february))
  
  (define-rule (rule-7 simple-goal-test-rules)
      (economy bad)
    <==
      (year 1993))
  
  (define (solve-simple-goal-test)
    (with-new-inference-environment
     (activate simple-goal-test-rules)
     (current-inference-trace #t)
     (assert '(month february))
     (assert '(year 1993))
     (let ((result (check '(bad-mood alison))))
       (printf "(check '(bad-mood alison)) = ~a ~n" result)
       (if (not (null? result))
           (printf "Alison is in a bad mood.~n")
           (printf "Alison is not (known to be) in a bad mood.~n")))))
  
  (solve-simple-goal-test)
  
  )