my first time Yesod. チュートリアルにそって、３ページを巡回するアプリケーションを作成

haskel_and_yesod.hs

{-# LANGUAGE TypeFamilies, QuasiQuotes, MultiParamTypeClasses,
             TemplateHaskell, OverloadedStrings #-}
import Yesod

data Links = Links

mkYesod "Links" [parseRoutes|
/ HomeR GET
/page1R Page1R GET
/page2R Page2R GET
|]

instance Yesod Links

getHomeR  = defaultLayout [whamlet|<a href=@{Page1R}>Go to page 1!|]
getPage1R = defaultLayout [whamlet|<a href=@{Page2R}>Go to page 2!|]
getPage2R = defaultLayout [whamlet|<a href=@{HomeR}>Go home!|]

main = warpDebug 3000 Links
{- and excute runhaskell filename.hs in terminal -}
{- access http://localhost:3000/ yay! -}