[web-devel] [Yesod] Need help resolving this compiler error.

[Greg Weber]

Hi Michael,

Can you send your question to the yesod google group?
groups.google.com/group/yesodweb

Thanks,
Greg Weber

On Thu, Nov 3, 2011 at 5:10 PM, Michael Litchard <michael at schmong.org>wrote:

> Specifically, I will be running this database query as one step of
> many in the process of generating the menu in a selectField.
>
> On Thu, Nov 3, 2011 at 4:57 PM, Michael Litchard <michael at schmong.org>
> wrote:
> > Going over the Yesod Book again, I realize I had it right the first
> > time. The database query needs to stay in the Handler. The question
> > then becomes, how do I get data structures inside a form from a
> > handler, when the only acceptable parameter seems to be an Html type?
> >
> > On Thu, Nov 3, 2011 at 4:52 PM, Michael Litchard <michael at schmong.org>
> wrote:
> >> I'm doing a database action, inside a Form action. I had wanted to do
> >> it inside a Handler, as I had figured out how to make it work. But I
> >> could not figure out how to pass the data the Form needs from the
> >> Handler. Here's the error, followed by the code I am trying to use.
> >>
> >>>Handler/Manager.hs:68:16:
> >>    No instance for (PersistBackend
> >>                       (YesodPersistBackend master0) (GGHandler sub0
> >> master0 IO)
> >>                                                                )
> >>  arising from a use of `isFree'
> >> Possible fix:
> >>  add an instance declaration for
> >>  (PersistBackend
> >>     (YesodPersistBackend master0) (GGHandler sub0 master0 IO))
> >> In a stmt of a 'do' expression: testFree <- isFree testDay
> >> In the expression:
> >>  do { pInfo <- liftIO getUIdata;
> >>       let products = V.toList $ V.map productACC $ fst pInfo
> >>           versions = V.toList $ V.map versionsACC $ snd pInfo
> >>           ....;
> >>       testFree <- isFree testDay;
> >>       (productRes, productView) <- mreq
> >>                                      (radioField products)
> >> "Placeholder" No
> >>                                                              thing;
> >>       .... }
> >> In an equation for `productForm':
> >>    productForm extra
> >>      = do { pInfo <- liftIO getUIdata;
> >>             let products = ...
> >>                 ....;
> >>             testFree <- isFree testDay;
> >>             .... }
> >>
> >>
> >>>Handler/Manager.hs:68:16:
> >> Couldn't match expected type `Control.Monad.Trans.RWS.Lazy.RWST
> >>                                (Maybe (Env, FileEnv), Scheduler,
> >> [Yesod.For
> >>                                                        m.Types.Lang])
> >>                                Enctype
> >>                                Ints
> >>                                (GGHandler Scheduler Scheduler IO)
> >>                                t0'
> >>            with actual type `GGHandler sub0 master0 monad0 Bool'
> >> In the return type of a call of `isFree'
> >> In a stmt of a 'do' expression: testFree <- isFree testDay
> >> In the expression:
> >>  do { pInfo <- liftIO getUIdata;
> >>       let products = V.toList $ V.map productACC $ fst pInfo
> >>           versions = V.toList $ V.map versionsACC $ snd pInfo
> >>           ....;
> >>       testFree <- isFree testDay;
> >>       (productRes, productView) <- mreq
> >>                                      (radioField products)
> >> "Placeholder" Nothing;
> >>
> >>>postManagerR :: Handler RepHtml
> >> postManagerR = do
> >>    ((res, widget), enctype) <- runFormPost productForm
> >>    dataInsert <- case (addEntry res) of
> >>                     Left blank ->  blank
> >>                     Right result -> result
> >> --    let testDay = C.fromGregorian 2011 12 27 -- I would prefer to
> >> have the code in the Handler if I could figure out how to get it to
> >> the Form? State Monad?
> >> --    testFree <- isFree testDay
> >>        defaultLayout [whamlet|
> >>    <p>Result:#{show dataInsert}
> >>      <form enctype=#{enctype}>
> >>          ^{widget}
> >>    |]
> >>
> >>>productForm :: Html
> >>            -> Form Scheduler Scheduler (FormResult SelectedProduct,
> Widget)
> >> productForm extra = do
> >>   pInfo <- liftIO getUIdata
> >>   let products = V.toList $ V.map productACC  $ fst pInfo
> >>       versions = V.toList $ V.map versionsACC $ snd pInfo
> >>       testDay = C.fromGregorian 2011 12 27
> >>   testFree <- isFree testDay
> >>   (productRes, productView) <- mreq (radioField products) "Placeholder"
> Nothing
> >>   versionInfo <- mapM generateVersionSelectFields versions
> >> --   (dateRes, dateView) <- mreq requestedDayField "Schedule" Nothing
> >>   (dateRes, dateView) <- mreq (jqueryDayField def
> >>                         { jdsChangeYear = True
> >>                         , jdsYearRange = "2011:2012"
> >>                         }) "Schedule" Nothing
> >>
> >>   let versionRes = map fst versionInfo
> >>       versionViews = map snd versionInfo
> >>       widget = do
> >>          toWidget [whamlet|
> >>  #{extra}
> >>  <p>
> >>    ^{fvInput productView}
> >>     $forall versionView <- versionViews
> >>        ^{fvInput versionView}
> >>    ^{fvInput dateView}
> >>    <input type=submit value="Request Test">
> >>  |]
> >>
> >>   return (makeSelected productRes versionRes dateRes, widget)
> >>
> >>>isFree day = do
> >>   match <- runDB $ selectList [TestStartDate ==. day,
> >>                        TestStatus !=. Passed,
> >>                        TestStatus !=. Failed] []
> >>   if (L.null match) then liftIOHandler (return True) else
> >> liftIOHandler (return False)
> >>
> >> I don't think the lack of an instance declaration is the real problem
> >> but an indication I am just doing it wrong. What 'it' is, is a mystery
> >> to me.
> >>
> >> ghci tells me this
> >>
> >>>isFree
> >>      :: (YesodPersist master,
> >>          PersistBackend
> >>            (YesodPersistBackend master) (GGHandler sub master IO),
> >>          Control.Monad.IO.Class.MonadIO monad) =>
> >>         Day -> GGHandler sub master monad Bool
> >>
> >> I believe I am using liftIOHandler correctly, I'm not sure what I am
> >> doing wrong. What I am sure of is it probably has to do with not
> >> understanding Yesod monads well enough. Feedback welcome.
> >>
> >
>
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