MonadBaseControl IO instance for Handlers - Snap Framework

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Message from discussion MonadBaseControl IO instance for Handlers
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Subject: Re: MonadBaseControl IO instance for Handlers
From: =?iso-8859-1?Q?Jurri=EBn_Stutterheim?= <j.stutterh...@me.com>
In-reply-to: <CAHZrzdqQfTLkESwO2rYurDVtdCbH_=io5Y5tvdsVMOf6p6G...@mail.gmail.com>
Date: Sun, 05 Feb 2012 15:11:33 +0100
Cc: Dmitry Dzhus <d...@dzhus.org>, s...@snapframework.com,
 Jasper Van der Jeugt <jasper...@gmail.com>
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 <CAHZrzdqQfTLkESwO2rYurDVtdCbH_=io5Y5tvdsVMOf6p6G...@mail.gmail.com>
To: Gregory Collins <g...@gregorycollins.net>
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I've made an attempt to port Snap to monad-control, but it broke the =
entire framework in non-obvious ways. It is possible to define a =
`MonadControlIO` instance for `Handler`, though (monad-control-0.2.x). =
That would allow you to use the original resource-pool. I didn't get =
around to writing instances for the latest version of monad-control =
though (I decided to switch back to `MonadCatchIO` instead). Here's the =
code I had for `MonadControlIO`:

    #if MIN_VERSION_monad_control(0,3,0)
 =09
    #else
    instance MonadControlIO (Handler b v) where
      liftControlIO f =3D liftBase (f return)
    #endif


Jurri=EBn

On 5 Feb 2012, at 11:46, Gregory Collins wrote:

> On Sun, Feb 5, 2012 at 10:45 AM, Dmitry Dzhus <d...@dzhus.org> wrote:
> How are you gentlemen?
>=20
> I'd like to switch to using Pool from resource-pool [1] package in my
> snaplet [2] to handle database connection pool. This requires my
> Handlers to have MonadBaseControl IO instance, whereas Snap provides
> MonadCatchIO. Seems like using resource-pool-catchio fork [3] could do
> the trick, but is there any chance to see MonadBaseControl support in
> Snap?
>=20
> [1]: http://hackage.haskell.org/package/resource-pool
> [2]: =
https://github.com/dzhus/snap-redis-crud/blob/master/src/RedisDB.hs
> [3]: http://hackage.haskell.org/package/resource-pool-catchio
>=20
> I think one of Jurri=EBn or Jasper was working on it, but it's =
actually not easy to do; there are little wrinkles in our MonadCatchIO =
instance which MonadBaseControl doesn't support. You're better off just =
lifting to IO and running your database code there.
>=20
> G
> --=20
> Gregory Collins <g...@gregorycollins.net>
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