我試着修改一個Yesod項目,並遇到了一個奇怪的錯誤。首先,我將介紹工作表單代碼,以及帶有錯誤信息的裸機代碼。爲什麼一個使用toWidget的工作,另一個不是
type PForm x = ProductConfig -> Html -> MForm ReScheduler ReScheduler (FormResult x, Widget)
工作代碼下一
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)
上面的代碼工作正常。這裏是破碎的代碼,然後是錯誤和一些觀察。
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) }
注意註釋掉硬編碼的小村莊代碼。這編譯好。這使我相信問題在於widgetFile
,而不是toWidget
。我在Yesod博客中指出,有時widgetFile
需要明確的:: Widget
類型簽名。我一直無法得到這個工作。也許這只是一個語法問題。反饋將受到歡迎。在此期間,我可以使用硬編碼的哈姆雷特。