Acid-State example

[ronslow]

Is it possible to provide an example of integration with Acid-State?

[Erik Hesselink]

What kind of integration are you looking for? It looks to me like you could just run any kind of acid-state transactions you want inside of a rest API.

[ronslow]

Hi Erik

Just an example of a Handler which executes a query on an AcidState
container

I'm finding the types quite difficult to manage.

Robert

On Tue, Dec 8, 2015 at 9:59 AM, Erik Hesselink [e-mail]
wrote:

What kind of integration are you looking for? It looks to me like you
could just run any kind of acid-state transactions you want inside of a
rest API.

—
Reply to this email directly or view it on GitHub
#143 (comment).

[Erik Hesselink]

I'm no expert on acid-state, but it looks like all the top level operations (query, update) are in IO. Since rest handlers run in MonadIO, I would think that using liftIO should be enough. So something like:

liftIO $ query acid SomeQuery

You'd need to get the AcidState from somewhere. The easiest thing is probably to run your rest handlers in ReaderT AcidState IO. Then at the top level of your application, you'd initialize acid-state, and call runReaderT api acid to pass it to your api.

Does that make sense? If it doesn't, can you paste a small example of what you're trying somewhere, together with the error message where you can't make it work?

[ronslow]

Thanks Erik

Yes, I thought that I would simplify as much as possible with respect to
the tutorial by using mkResourceId but this in fact led to greater
complexity in matching types between Rest and Acid-State.

I have followed the tutorial more closely, using mkResourceReader, and as
you say this uses a ReaderT to allow Acid-State to play in IO:

resource :: AcidState Diary -> Resource IO (ReaderT BookingId IO) BookingId
Void Void
resource diary = mkResourceReader { R.name = "bookingid"

                                                         , R.get = Just

(getBooking diary)
}

getBooking :: AcidState Diary -> Handler (ReaderT BookingId IO)
getBooking diary = mkIdHandler jsonO $ _ bid -> liftIO $ query diary
(GetBooking bid)

For the moment I am simply passing the AcidState as a parameter, but of
course eventually this will be better to pass in by of ReaderT

Robert

On Tue, Dec 8, 2015 at 10:17 AM, Erik Hesselink [e-mail]
wrote:

I'm no expert on acid-state, but it looks like all the top level
operations (query, update) are in IO. Since rest handlers run in MonadIO,
I would think that using liftIO should be enough. So something like:

liftIO $ query acid SomeQuery

You'd need to get the AcidState from somewhere. The easiest thing is
probably to run your rest handlers in ReaderT AcidState IO. Then at the
top level of your application, you'd initialize acid-state, and call runReaderT
api acid to pass it to your api.

Does that make sense? If it doesn't, can you paste a small example of what
you're trying somewhere, together with the error message where you can't
make it work?

—
Reply to this email directly or view it on GitHub
#143 (comment).

[Erik Hesselink]

Ah, I see! The ReaderT I meant wasn't the one constructed by mkResourceReader. That creates an additional layer containing the id of the resource being server. I was talking about the top level monad (the m in the top level Resource you're defining). In the tutorial this is always assumed to be IO. But it doesn't have to be, and I think in your case it should be ReaderT AcidState IO. Then the code under "running it" would be slightly different: instead of apiToHandler' liftIO api, it should be something like apiTohandler' (liftIO . flip runReaderT acid) api.

But your current method should also work, it's just a bit more explicit about passing around the AcidState. Are you still having problems, or does it work now?

[ronslow]

All working, thanks Erik.

On Tue, Dec 8, 2015 at 11:51 AM, Erik Hesselink [e-mail]
wrote:

Ah, I see! The ReaderT I meant wasn't the one constructed by
mkResourceReader. That creates an additional layer containing the id of
the resource being server. I was talking about the top level monad (the m
in the top level Resource you're defining). In the tutorial this is
always assumed to be IO. But it doesn't have to be, and I think in your
case it should be ReaderT AcidState IO. Then the code under "running it"
would be slightly different: instead of apiToHandler' liftIO api, it
should be something like apiTohandler' (liftIO . flip runReaderT acid) api
.

But your current method should also work, it's just a bit more explicit
about passing around the AcidState. Are you still having problems, or
does it work now?

—
Reply to this email directly or view it on GitHub
#143 (comment).

[Erik Hesselink]

Great!