f-to-c3.rkt
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#lang syndicate
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;; After the Fahrenheit-to-Celsius converter example in "Fabrik - A
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;; Visual Programming Environment", Ingalls, Wallace, Chow, Ludolph
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;; and Doyle, OOPSLA 1988.
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(struct temperature (unit value) #:prefab)
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(struct set-temperature (unit value) #:prefab)
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(spawn #:name 'track-celsius
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(field [temp 0])
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(assert (temperature 'C (temp)))
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(on (message (set-temperature 'C $new-temp)) (temp new-temp)))
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(spawn #:name 'track-fahrenheit
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(field [temp 32])
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(assert (temperature 'F (temp)))
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(on (message (set-temperature 'F $new-temp)) (temp new-temp)))
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(spawn #:name 'convert-C-to-F
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(on (asserted (temperature 'C $other-temp))
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(send! (set-temperature 'F (+ (* other-temp 9/5) 32)))))
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(spawn #:name 'convert-F-to-C
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(on (asserted (temperature 'F $other-temp))
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(send! (set-temperature 'C (* (- other-temp 32) 5/9)))))
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(spawn (on (asserted (temperature $unit $value))
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(printf "Temperature in ~a is ~a\n" unit (exact->inexact value))))
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(spawn (on (asserted (observe (set-temperature _ _)))
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;; (send! (set-temperature 'C 20))
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(send! (set-temperature 'F 90))
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))
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