40 lines
1.4 KiB
Racket
40 lines
1.4 KiB
Racket
#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 version) #:prefab)
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(struct set-temperature (unit value version) #:prefab)
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(spawn #:name 'track-celsius
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(field [temp 0] [version 0])
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(assert (temperature 'C (temp) (version)))
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(on (message (set-temperature 'C $new-temp $v))
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(when (> v (version))
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(temp new-temp)
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(version v))))
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(spawn #:name 'track-fahrenheit
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(field [temp 32] [version 0])
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(assert (temperature 'F (temp) (version)))
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(on (message (set-temperature 'F $new-temp $v))
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(when (> v (version))
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(temp new-temp)
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(version v))))
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(spawn #:name 'convert-C-to-F
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(on (asserted (temperature 'C $other-temp $v))
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(send! (set-temperature 'F (+ (* other-temp 9/5) 32) v))))
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(spawn #:name 'convert-F-to-C
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(on (asserted (temperature 'F $other-temp $v))
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(send! (set-temperature 'C (* (- other-temp 32) 5/9) v))))
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(spawn (on (asserted (temperature $unit $value $v))
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(printf "Temperature in ~a at version ~a is ~a\n" unit v (exact->inexact value))))
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(spawn (on (asserted (observe (set-temperature _ _ _)))
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(send! (set-temperature 'C 20 1))
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(send! (set-temperature 'F 90 2))
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))
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