This example uses the data-object-yaml package to display YAML files as cleaned-up HTML. If you've read through the other tutorials, this one should be easy to follow.
> {-# LANGUAGE TypeFamilies, QuasiQuotes, TemplateHaskell, MultiParamTypeClasses #-}
> import Yesod
> import Data.Object
> import Data.Object.Yaml
> import qualified Data.ByteString as B
> import qualified Data.ByteString.Lazy as L
> data PY = PY
> type Handler = GHandler PY PY
> mkYesod "PY" [$parseRoutes|
> / Homepage GET POST
> |]
> instance Yesod PY where approot _ = ""
> template :: Maybe (Hamlet url) -> Hamlet url
> template myaml = [$hamlet|
> !!!
>
>
>
>
> Pretty YAML
> <body>
> <form method="post" action="" enctype="multipart/form-data" .>
> \File name:
> <input type="file" name="yaml">
> <input type="submit">
> $maybe yaml <- myaml
> <div>^{yaml}
> |]
> getHomepage :: Handler RepHtml
> getHomepage = hamletToRepHtml $ template Nothing
> postHomepage :: Handler RepHtml
> postHomepage = do
> (_, files) <- runRequestBody
> fi <- case lookup "yaml" files of
> Nothing -> invalidArgs ["yaml: Missing input"]
> Just x -> return x
> so <- liftIO $ decode $ B.concat $ L.toChunks $ fileContent fi
> hamletToRepHtml $ template $ Just $ objToHamlet so
> objToHamlet :: StringObject -> Hamlet url
> objToHamlet (Scalar s) = [$hamlet|#{s}|]
> objToHamlet (Sequence list) = [$hamlet|
> <ul
> $forall o <- list
> <li>^{objToHamlet o}
> |]
> objToHamlet (Mapping pairs) = [$hamlet|
> <dl
> $forall pair <- pairs
> <dt>#{fst pair}
> <dd>^{objToHamlet $ snd pair}
> |]
> main :: IO ()
> main = warpDebug 3000 PY