On Mon, Jul 11, 2011 at 6:27 PM, Michael Orlitzky
On 07/10/11 15:37, Felipe Almeida Lessa wrote:
You don't need to do it, it is already done =). See the pool package by Michael Snoyman on Hackage [1]. More specifically, see createPoolCheckAlive [2].
Cheers,
[1] http://hackage.haskell.org/package/pool [2] http://hackage.haskell.org/packages/archive/pool/0.1.0.2/doc/html/Data-Pool....
How do people use this stuff? The README is empty, there's no documentation, and none of the functions are commented. I'm forced to conclude that there are people capable of looking at this,
createPoolCheckAlive :: MonadControlIO m => IO a -> (a -> IO ()) -> Int -> (Pool a -> m b) -> (a -> IO Bool) -> m b
and knowing immediately what it does.
I'm still a beginner, and I don't think I have a use for this package (what does it do?), but I've run into similar situations with other packages and would genuinely like to know (as opposed to just complain about it).
Author of the package speaking. I agree, that's a problem :). I've just uploaded a new version[1] that is properly documented, though it will take a bit for Hackage to generates the Haddocks. As Brandon said, the reason this wasn't documented in the first place is that it was an internally used module for Persistent that I decided after the fact to release separately. As for Bryan's resource-pool: currently I would strongly recommend *against* using it for any purpose. It is based on MonadCatchIO-transformers[2], which is a subtly broken package. In particular, when I tried using it for pool/persistent in the first place, I ended up with double-free bugs from SQLite. As an abridged history, I ended up writing a replacement called MonadInvertIO, which later was superceded by MonadPeelIO[3] and MonadControlIO[4]. The latter two packages are both much more correct that MonadCatchIO, and either one should be used in its place. I did email Bryan about this a bit ago, but he didn't get back (he *is* a very busy guy). Ideally, I think that we don't need to have both pool and resource-pool, but such is the situation right now. Michael [1] http://hackage.haskell.org/package/pool-0.1.0.3 [2] http://hackage.haskell.org/package/MonadCatchIO-transformers-0.2.2.2 [3] http://hackage.haskell.org/package/monad-peel [4] http://hackage.haskell.org/package/monad-control-0.2.0.1