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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Ternary-logic/Racket/ternary-logic.rkt Normal file
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#lang typed/racket
; to avoid the hassle of adding a maybe value that is as special as
; the two standard booleans, we'll use symbols to make our own
(define-type trit (U 'true 'false 'maybe))
(: not (trit -> trit))
(define (not a)
(case a
[(true) 'false]
[(maybe) 'maybe]
[(false) 'true]))
(: and (trit trit -> trit))
(define (and a b)
(case a
[(false) 'false]
[(maybe) (case b
[(false) 'false]
[else 'maybe])]
[(true) (case b
[(true) 'true]
[(maybe) 'maybe]
[(false) 'false])]))
(: or (trit trit -> trit))
(define (or a b)
(case a
[(true) 'true]
[(maybe) (case b
[(true) 'true]
[else 'maybe])]
[(false) (case b
[(true) 'true]
[(maybe) 'maybe]
[(false) 'false])]))
(: ifthen (trit trit -> trit))
(define (ifthen a b)
(case b
[(true) 'true]
[(maybe) (case a
[(false) 'true]
[else 'maybe])]
[(false) (case a
[(true) 'false]
[(maybe) 'maybe]
[(false) 'true])]))
(: iff (trit trit -> trit))
(define (iff a b)
(case a
[(maybe) 'maybe]
[(true) b]
[(false) (not b)]))
(for: : Void ([a (in-list '(true maybe false))])
(printf "~a ~a = ~a~n" (object-name not) a (not a)))
(for: : Void ([proc (in-list (list and or ifthen iff))])
(for*: : Void ([a (in-list '(true maybe false))]
[b (in-list '(true maybe false))])
(printf "~a ~a ~a = ~a~n" a (object-name proc) b (proc a b))))