[Haskell-cafe] Caching the Result of a Transaction?
jake.mcarthur at gmail.com
Sun Apr 27 11:05:06 EDT 2008
On Apr 27, 2008, at 9:36 AM, Conal Elliott wrote:
> First, I think we want readTMVar instead of takeTMVar in newTIVal.
I don't see any reason it would hurt to use takeTMVar, and I suspect
the garbage collector might be slightly happier this way since it
potentially means once less reference to the data stored in the TMVar.
> I think we *do* want unsafeNewEmptyTMVar inlined. Here's a
> convenient caching wrapper:
> cached :: STM a -> TIVal a
> cached m = TIVal m (unsafePerformIO newEmptyTMVarIO)
> The instances are then lovely:
> instance Functor TIVal where
> f `fmap` tiv = cached (f `fmap` force tiv)
> instance Applicative TIVal where
> pure x = cached (pure x)
> ivf <*> ivx = cached (force ivf <*> force ivx)
> instance Monad TIVal where
> return x = cached (return x)
> tiv >>= k = cached (force tiv >>= force . k)
Yes, this is essentially what I am working with in Reaction at the
moment. It seems to be working great, but I have not specifically
tested the caching behavior yet, only that it doesn't screw up what I
had working in the first place.
I must admit that I think I don't fully understand the implications of
inlining vs. not inlining unsafePerformIO.
More information about the Haskell-Cafe