Yesod表单中的generateForm帖子类型错误

Question

我收到类型错误

Estuary0b.hs:112:53:
    Couldn't match type `HandlerT Site IO' with `WidgetT Site IO'
    Expected type: Text.Blaze.Internal.Markup
                   -> MForm (WidgetT Site IO) (FormResult Course, WidgetT Site IO ())
      Actual type: Text.Blaze.Internal.Markup
                   -> Control.Monad.Trans.RWS.Lazy.RWST
                        (Maybe (Env, FileEnv), HandlerSite (HandlerT Site IO), [Lang])
                        Enctype
                        Ints
                        (HandlerT Site IO)
                        (FormResult Course, WidgetT (HandlerSite (HandlerT Site IO)) IO ())
    In the first argument of `generateFormPost', namely
      `add_course_form'
    In a stmt of a 'do' block:
      (form_widget, form_enctype) <- generateFormPost add_course_form
    In the second argument of `($)', namely
      `do { setTitle "Estuary - Courses";
            (form_widget, form_enctype) <- generateFormPost add_course_form;
            do { (Yesod.Core.Widget.asWidgetT . toWidget)
                   ((Text.Blaze.Internal.preEscapedText . Data.Text.pack)
                      "<h1>Courses</h1>\
                      \<table><tr><th>Name</th>\
                      \<th>Accreditation</th>\
                      \<th>Specification</th>\
                      \<th>Scheme of work</th>\
                      \<th>Past papers</th>\
                      \</tr>");
                 Data.Foldable.mapM_
                   (\ (Course cname_a5mw aname_a5mx __a5my __a5mz __a5mA) -> ...
)
                   courses;
                 .... } }'

当我尝试编译以下内容时：

data Course = Course {
    _course_name :: !Text,
    _accreditor :: !Text,
    _spec :: !ByteString,
    _sow :: !ByteString,
  _past_exams :: ![ByteString]
    }
    deriving (Eq, Ord, Data, Typeable)
deriveSafeCopy 0 'base ''Course

mkYesod "Site" [parseRoutes|

  / Home GET


  /courses Courses GET POST


  |]


getHome :: Handler Html
getHome = do
  defaultLayout [whamlet|<h1>Estuary|]


getCourses :: Handler Html
getCourses = do
  site <- getYesod
  courses <- fmap IxSet.toList $ query' (_db site) All_courses
  defaultLayout $ do
    setTitle "Estuary - Courses"
    (form_widget, form_enctype) <- generateFormPost add_course_form
    [whamlet|
      <h1>Courses
      <table>
        <tr>
          <th>Name
          <th>Accreditation
          <th>Specification
          <th>Scheme of work
          <th>Past papers
        $forall (Course cname aname _ _ _) <- courses
          <tr>
            <td>#{cname}
            <td>#{aname}
            <td><a href="">Download</a>
            <td><a href="">Download</a>
      <h2>Add a new course
      <form method=post action=@{Courses} enctype=#{form_enctype}>
        ^{form_widget}
        <input type=submit value=Add_course>|]



add_course_form = renderDivs $ Course
  <$> areq textField "Course name" Nothing
  <*> areq textField "Accredditation" Nothing
  <*> pure Bytes.empty
  <*> pure Bytes.empty
  <*> pure []

postCourses :: Handler Html
postCourses = do
  ((result, _), _) <- runFormPost add_course_form
  case result of
    FormSuccess course -> do
      site <- getYesod
      update' (_db site) (Add_course course)
    _ -> return ()
  redirect Courses

有人可以帮忙吗？

Answer 1

generateFormPost旨在在Handler monad中运行，而不是Widget monad。你可以：

1. 将generate阻止移至defaultLayout阻止之外。
2. 在handlerToWidget。
前面添加generateFormPost来电