I'm afraid that this is deep voodoo to me.
MyMonad is defined as follows:
newtype MyMonad a = MyM {
runA :: ReaderT MyGlobals (StateT MyResponse IO) a
} deriving (Monad, MonadReader MyGlobals,
MonadState MyResponse)
When I try to call one of the functions in this Monad, eg.
myFunc :: String -> MyMonad ()
within a splice function, eg.
mySplice :: Splice MyMonad
then I get a compile error unless I use lift.
What can I do to skip lift?
Kevin
--- On Tue, 6/15/10, MightyByte <[email protected]> wrote:
> From: MightyByte <[email protected]>
> Subject: Re: [Snap Framework] Splice functions and a custom monad
> To: "Kevin Jardine" <[email protected]>
> Cc: [email protected]
> Date: Tuesday, June 15, 2010, 2:10 PM
> The passthrough involves instances of
> common monad classes. If
> MyMonad has a MonadState instance, then you don't need to
> use lift to
> get to the MonadState functions. TemplateMonad
> defines an instance
> that does the lift for you. This is new in Heist
> 0.2. It works for
> most of the most common monad type classes that you might
> use.
> MonadState, MonadReader, MonadPlus, etc. You can see
> the list here:
>
> http://github.com/snapframework/heist/blob/master/src/Text/Templating/Heist/Types.hs
>
> On Tue, Jun 15, 2010 at 2:12 AM, Kevin Jardine <[email protected]>
> wrote:
> > Yes, thanks. I do need lift to access MyMonad though.
> I understand that there is something called a passthrough
> that might remove this requirement. Do you know how that
> works?
> >
> > Kevin
> >
> > --- On Tue, 6/15/10, MightyByte <[email protected]>
> wrote:
> >
> >> From: MightyByte <[email protected]>
> >> Subject: Re: [Snap Framework] Splice functions and
> a custom monad
> >> To: "Kevin Jardine" <[email protected]>
> >> Cc: [email protected]
> >> Date: Tuesday, June 15, 2010, 3:21 AM
> >> Kevin,
> >>
> >> You mentioned two different error messages
> above. I
> >> just wanted to
> >> verify that both of them are taken care of now?
> >>
> >> On Mon, Jun 14, 2010 at 6:19 PM, Kevin Jardine
> <[email protected]>
> >> wrote:
> >> > As MonadIO was no longer being automatically
> derived
> >> without mtl, I added these lines:
> >> >
> >> > instance MonadIO MyMonad where
> >> > liftIO m = MyM (liftIO m)
> >> >
> >> > and this seems to have fixed the problem. I
> no longer
> >> need mtl and I can use Heist as needed!
> >> >
> >> > --- On Mon, 6/14/10, Kevin Jardine <[email protected]>
> >> wrote:
> >> >
> >> >> From: Kevin Jardine <[email protected]>
> >> >> Subject: [Snap Framework] Splice
> functions and a
> >> custom monad
> >> >> To: [email protected]
> >> >> Date: Monday, June 14, 2010, 10:52 PM
> >> >> I'd like to run Heist template splice
> >> >> functions in my own custom monad (not
> Snap).
> >> >>
> >> >> I can define a splice function as:
> >> >>
> >> >> mySplice :: Splice MyMonad
> >> >>
> >> >> However, when I try to call functions
> that return
> >> values in
> >> >> my monad in mySplice, I get a compile
> error:
> >> >>
> >> >> Couldn't match expected type
> TemplateMonad MyMonad
> >> a
> >> >> against inferred type MyMonad ()
> >> >>
> >> >> I've seen an example in the Heist
> documentation
> >> where the
> >> >> inner MyMonad is accessed using lift. But
> when I
> >> try that, I
> >> >> get another compile error:
> >> >>
> >> >> No instance for (MonadTrans
> TemplateMonad)
> >> >> arising from the use of 'lift'
> >> >>
> >> >> Gregory Collins advised replacing mtl
> with
> >> monads-fd and
> >> >> transformers.
> >> >>
> >> >> However, this breaks my custom monad (eg.
> MonadIO
> >> is no
> >> >> longer automatically derived).
> >> >>
> >> >> How do I get this to work?
> >> >>
> >> >> Kevin
> >> >>
> >> >>
> >> >>
> >> >>
> _______________________________________________
> >> >> Snap mailing list
> >> >> [email protected]
> >> >> http://mailman-mail5.webfaction.com/listinfo/snap
> >> >>
> >> >
> >> >
> >> >
> >> >
> _______________________________________________
> >> > Snap mailing list
> >> > [email protected]
> >> > http://mailman-mail5.webfaction.com/listinfo/snap
> >> >
> >>
> >
> >
> >
> >
>
_______________________________________________
Snap mailing list
[email protected]
http://mailman-mail5.webfaction.com/listinfo/snap
