yesod how to solve this error? - haskell

Question

I am just started with Yesod, I am following this tutorial:http://yannesposito.com/Scratch/en/blog/Yesod-tutorial-for-newbies/
I get this error:
Handler/Blog.hs:32:17:
Couldn't match type `handler' with `GHandler App App'
`handler' is a rigid type variable bound by
the type signature for postBlogR :: handler RepHtml
at Handler/Blog.hs:29:14
Expected type: handler [Entity Article]
Actual type: GHandler App App [Entity Article]
In a stmt of a 'do' block:
articles <- runDB $ selectList [] [Desc ArticleTitle]
In the expression:
do { articles <- runDB $ selectList [] [Desc ArticleTitle];
(articleWidget, enctype) <- generateFormPost entryForm;
defaultLayout $ do { $(widgetFile "articles") } }
In an equation for `postBlogR':
postBlogR
= do { articles <- runDB $ selectList [] [Desc ArticleTitle];
(articleWidget, enctype) <- generateFormPost entryForm;
defaultLayout $ do { ... } }
this is my Blog.hs:
module Handler.Blog
( getBlogR
, postBlogR
)
where
import Import
-- to use Html into forms
import Yesod.Form.Nic (YesodNic, nicHtmlField)
instance YesodNic App
entryForm :: Form Article
entryForm = renderDivs $ Article
<$> areq textField "Title" Nothing
<*> areq nicHtmlField "Content" Nothing
-- The view showing the list of articles
getBlogR :: Handler Html
getBlogR = do
-- Get the list of articles inside the database.
articles <- runDB $ selectList [] [Desc ArticleTitle]
-- We'll need the two "objects": articleWidget and enctype
-- to construct the form (see templates/articles.hamlet).
(articleWidget, enctype) <- generateFormPost entryForm
defaultLayout $ do
$(widgetFile "articles")
postBlogR :: handler RepHtml
postBlogR = do
-- Get the list of articles inside the database.
articles <- runDB $ selectList [] [Desc ArticleTitle]
-- We'll need the two "objects": articleWidget and enctype
-- to construct the form (see templates/articles.hamlet).
(articleWidget, enctype) <- generateFormPost entryForm
defaultLayout $ do
$(widgetFile "articles")
my routes:
/static StaticR Static getStatic
/auth AuthR Auth getAuth
/favicon.ico FaviconR GET
/robots.txt RobotsR GET
/ HomeR GET POST
/echo/#Text EchoR GET
/mirror MirrorR GET POST
/blog BlogR GET POST
/blog/#ArticleId ArticleR GET
and my models:
User
ident Text
password Text Maybe
UniqueUser ident
Email
email Text
user UserId Maybe
verkey Text Maybe
UniqueEmail email
Article
title Text
content Html
deriving
-- By default this file is used in Model.hs (which is imported by Foundation.hs)

Answer 1

I think, you just have to fix your type signature for postBlogR to Handler RepHtml. Names starting with lower case letters are reserved for type variables in type signatures, so it cannot be deduced right here.