Why does one use of toWidget work, and the other doesn't
Frage
I tried modifying a Yesod project, and came across a weird error. First I will present the working form code, and the bare-bones broken code with error message.
type PForm x = ProductConfig ->
Html ->
MForm ReScheduler ReScheduler (FormResult x, Widget)
working code next
productForm :: PForm SelectedProduct
productForm config extra = do
let pInfo' = pInfo config
aDays' = aDays config
products = (catMaybes . pNametoText) pInfo'
versions' = map consVersionPair pInfo'
productInfo <- mapM generateSelectFields versions'
(dateRes, dateView) <- mreq (selectField aDays') "placeHolder" Nothing
(mailRes, mailView) <- mreq emailField "E-Mail Address" Nothing
(noteRes, noteView) <- mreq textareaField
"Notes"
Nothing
let productVersion = reduceFormResults $
map flagSelected $
map fst productInfo
versionViews = map snd productInfo
let widget =
toWidget $(widgetFile "firmware") :: Widget
return (makeSelected productVersion dateRes mailRes noteRes, widget)
The above code works fine. Here's the broken code, followed by the error and some observations.
type RForm x = [KeyJobPair] ->
Html ->
MForm ReScheduler ReScheduler (FormResult x, Widget)
statusForm :: RForm ModData
statusForm kjPairs extra = do
-- let bPairs = buttonPairs kjPairs
-- statusPairs = map (pack . show &&& id) $
-- ([minBound .. maxBound] :: [Status])
-- (jobRes,jobView) <- mreq (radioField bPairs) "Scheduled Jobs" Nothing
-- (mailRes, mailView) <- mreq emailField "E-Mail Address" Nothing
-- (noteRes, noteView) <- mreq textareaField "Notes" Nothing
-- (statusRes, statusView) <- mreq (selectField statusPairs) "Status" Nothing
-- let widget = toWidget [hamlet|<p> testing |]
let widget = (toWidget $(widgetFile "status" )) :: Widget
return (ModData <$> undefined <*> undefined <*> undefined, widget)
Handler/Manager.hs:109:19:
No instance for (ToWidget
ReScheduler ReScheduler (GGWidget master0 m0 ()))
arising from a use of `toWidget'
Possible fix:
add an instance declaration for
(ToWidget ReScheduler ReScheduler (GGWidget master0 m0 ()))
In the expression: (toWidget ($(widgetFile "status"))) :: Widget
In an equation for `widget':
widget = (toWidget ($(widgetFile "status"))) :: Widget
In the expression:
do { let widget = ...;
return
(ModData <$> undefined <*> undefined <*> undefined, widget) }
Note the commented out hard-coded hamlet code. This compiles fine. This leads me to believe the problem lies with widgetFile
, not toWidget
. I noted in the Yesod blog, that sometimes widgetFile
wants an explicit :: Widget
type signature. I haven't been able to get this to work. Maybe this is just a syntax problem. Feedback would be welcome. In the meantime I can just use hardcoded Hamlet.
Keine korrekte Lösung