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(;module:
lux
(lux [io]
(control monad)
(concurrency ["A" atom])
[compiler]
(macro ["s" syntax #+ syntax:])))
(type: #export (Thunk a)
(-> [] a))
(def: #hidden (freeze' generator)
(All [a] (-> (-> [] a) (-> [] a)))
(let [cache (: (A;Atom (Maybe ($ +0)))
(A;atom #;None))]
(lambda [_]
(case (io;run (A;get cache))
(#;Some value)
value
_
(let [value (generator [])]
(exec (io;run (A;compare-and-swap _ (#;Some value) cache))
value))))))
(syntax: #export (freeze expr)
(do @
[g!arg (compiler;gensym "")]
(wrap (list (` (freeze' (lambda [(~ g!arg)] (~ expr))))))))
(def: #export (thaw thunk)
(All [a] (-> (Thunk a) a))
(thunk []))
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