Developing Web Apps with Haskell and Yesod, 2nd Edition

Chapter 22. Blog: i18n, Authentication, Authorization, and Database

This chapter presents a simple blog app. It allows an admin to add blog posts via a rich text editor (nicedit), allows logged-in users to comment, and has full i18n support. It is also a good example of using a Persistent database, leveraging Yesod’s authorization system, and using templates.

It is generally recommended to place templates, Persist entity definitions, and routing in separate files, but we’ll keep it all in one file here for convenience. The one exception you’ll see will be i18n messages.

We’ll start off with our language extensions. In scaffolded code, the language extensions are specified in the cabal file, so you won’t need to put this in your individual Haskell files:

{-# LANGUAGE OverloadedStrings, TypeFamilies, QuasiQuotes,
             TemplateHaskell, GADTs, FlexibleContexts,
             MultiParamTypeClasses, DeriveDataTypeable,
             GeneralizedNewtypeDeriving, ViewPatterns #-}

Now our imports:

import Yesod
import Yesod.Auth
import Yesod.Form.Nic (YesodNic, nicHtmlField)
import Yesod.Auth.BrowserId (authBrowserId, def)
import Data.Text (Text)
import Network.HTTP.Client.TLS (tlsManagerSettings)
import Network.HTTP.Conduit (Manager, newManager)
import Database.Persist.Sqlite
    ( ConnectionPool, SqlBackend, runSqlPool, runMigration
    , createSqlitePool, runSqlPersistMPool
    )
import Data.Time (UTCTime, getCurrentTime)
import Control.Applicative ((<$>), (<*>), pure)
import Data.Typeable (Typeable)
import Control.Monad.Logger ...