112 lines
4.6 KiB
Racket
112 lines
4.6 KiB
Racket
#lang prospect
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(require racket/set)
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;; `binding` tuples associate keys with values at a certain version.
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;; versions start at 0 and increase by 1 with every successful update.
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(struct binding (key version value) #:transparent)
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;; `update` tuples request a binding update.
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(struct update (binding) #:transparent)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(define observation-projector (compile-projection (observe (binding (?!) ? ?))))
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(define update-projector (compile-projection (update (?! (binding ? ? ?)))))
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(struct db-state (bindings observed-keys) #:transparent)
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(define (lookup-binding bindings key)
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(hash-ref bindings key (lambda () (binding key -1 (void)))))
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(define ((process-suggestion suggestion) state)
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(match-define (db-state bindings observed-keys) state)
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(match-define (binding key suggested-version _) suggestion)
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(define old-binding (lookup-binding bindings key))
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(match-define (binding _ current-version _) old-binding)
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(if (= suggested-version (+ current-version 1))
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(transition (struct-copy db-state state
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[bindings (hash-set bindings key suggestion)])
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(when (set-member? observed-keys key)
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(patch-seq (retract old-binding)
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(assert suggestion))))
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(transition state '())))
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(define ((adjust-observations added-observations removed-observations) state)
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(match-define (db-state bindings observed-keys) state)
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(transition (struct-copy db-state state
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[observed-keys (set-union added-observations
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(set-subtract observed-keys
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removed-observations))])
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(list (for/list [(key (in-set removed-observations))]
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(retract (binding key ? ?)))
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(for/list [(key (in-set added-observations))]
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(when (hash-has-key? bindings key)
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(assert (lookup-binding bindings key)))))))
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(define (db)
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(spawn (lambda (e old-state)
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(match e
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[(? patch? p)
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(define-values (added-observations removed-observations)
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(patch-project/set/single p observation-projector))
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(define added-updates (matcher-project/set/single (patch-added p) update-projector))
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(transition-bind (adjust-observations added-observations removed-observations)
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(for/fold [(t (transition old-state '()))]
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[(suggestion (in-set added-updates))]
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(transition-bind (process-suggestion suggestion) t)))]
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[_ #f]))
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(db-state (hash) (set))
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(sub (observe (binding ? ? ?)))
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(sub (update (binding ? ? ?)))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(define binding-projector (compile-projection (?! (binding ? ? ?))))
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(define (async-update key version value on-complete on-conflict)
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(spawn (lambda (e s)
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(match e
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[(? patch? p)
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(match (set->list (matcher-project/set/single (patch-added p) binding-projector))
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['() #f]
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[(list (binding _ (== version) (== value)))
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(quit (on-complete))]
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[(list (binding _ (== (- version 1)) _))
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#f]
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[(list (binding _ other-version other-value))
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(quit (on-conflict key version value other-version other-value))])]
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[_ #f]))
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(void)
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(assert (update (binding key version value)))
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(sub (binding key ? ?))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(db)
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(define (monitor key)
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(spawn (lambda (e s)
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(match e
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[(? patch? p)
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(define n (matcher-project/set/single (patch-added p) (compile-projection (?!))))
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(for [(b n)] (printf "binding update: ~v\n" b))
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#f]
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[_ #f]))
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(void)
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(sub (binding key ? ?))))
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(monitor 'a)
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(monitor 'b)
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(async-update 'a 0 0
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(lambda () (async-update 'a 1 1
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(lambda () '())
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(lambda args (error 'conflict "at a/1"))))
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(lambda args (error 'conflict "at a/0")))
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(async-update 'b 0 0
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(lambda () (async-update 'b 0 1
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(lambda () '())
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(lambda args '())))
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(lambda args (error 'conflict "at b/0")))
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