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optimized preference lookup (one hash lookup in all cases except for the first.)

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svn: r14727

original commit: 7d93d3b539342184886f7f0433fc8ae1f71cb3a9
This commit is contained in:
Eli Barzilay 2009-05-06 04:07:23 +00:00
parent f5f5cf90aa
commit bc668b4652
1 changed files with 17 additions and 15 deletions
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32
collects/framework/preferences.ss
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@ -80,23 +80,25 @@ the state transitions / contracts are:
;; return the current value of the preference `p'
;; exported
(define (preferences:get p)
(define v (hash-ref preferences p none))
(cond
;; if this is found, we can just return it immediately
[(not (eq? v none))
v]
;; first time reading this, check the file & unmarshall value, if
;; it's not there, use the default
[(pref-default-set? p)
(unless (hash-has-key? preferences p)
;; first time reading this, check the file, unmarshall if required
(let/ec k
;; if there is no preference saved, we just don't do anything.
;; the code below notices this case.
(let ([marshalled ((preferences:low-level-get-preference)
(add-pref-prefix p) (λ () (k (void))))])
(hash-set! preferences p (unmarshall-pref p marshalled)))))
;; if it still isn't set, take the default value
(unless (hash-has-key? preferences p)
(hash-set! preferences p (default-value (hash-ref defaults p))))
(hash-ref preferences p)]
(let* (;; try to read the preferece from the preferences file
[v ((preferences:low-level-get-preference)
(add-pref-prefix p) (λ () none))]
[v (if (eq? v none)
;; no value read, take the default value
(default-value (hash-ref defaults p))
;; found a saved value, unmarshall it
(unmarshall-pref p marshalled))])
;; set the value for future reference and return it
(hash-set! preferences p v)
v)]
[(not (pref-default-set? p))
(raise-unknown-preference-error
'preferences:get