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deque-blog/selectAsync.hs

Created April 17, 2018 15:33
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selectAsync.hs
select :: IRequest req a => req a -> AsyncFetch req a
select req = AsyncFetch $ \cacheVar -> do
cache <- takeMVar cacheVar
case lookupCache req cache of
Just var -> do
putMVar cacheVar cache
pure var
Nothing -> do
var <- fetch req
putMVar cacheVar (insertCache req var cache)
pure var
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