36 lines
1.2 KiB
Racket
36 lines
1.2 KiB
Racket
#lang prospect
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;; Hello-worldish "bank account" example.
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(struct account (balance) #:prefab)
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(struct alter-balance-by (amount) #:prefab)
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(spawn (lambda (e balance)
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(match e
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[(message (alter-balance-by amount))
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(define new-balance (+ balance amount))
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(transition new-balance
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(patch-seq (retract (account balance))
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(assert (account new-balance))))]
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[_ #f]))
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0
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(patch-seq (assert (observe (alter-balance-by ?)))
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(assert (account 0))))
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(spawn (lambda (e s)
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(match e
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[(patch added removed)
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(for [(balance (matcher-project/set/single added (compile-projection (account (?!)))))]
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(printf "Balance changed to ~a\n" balance))
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#f]
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[_ #f]))
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(void)
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(assert (observe (account ?))))
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(spawn (lambda (e s)
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(if (and (patch? e) (matcher-non-empty? (patch-added e)))
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(quit (list (message (alter-balance-by +100))
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(message (alter-balance-by -30))))
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#f))
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(void)
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(assert (observe (observe (alter-balance-by ?)))))
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