Example of Yesod's fileField

fileFieldTest.hs

{-# LANGUAGE QuasiQuotes
           , OverloadedStrings 
           , TypeFamilies
           #-}

import Yesod
import Control.Applicative

data Test = Test

data Params = Params
  { minNumber :: Int
  , maxNumber :: Int
  , singleWord :: String
  , pluralWord :: String
  , fileTest :: FileInfo
  }
  deriving (Show)

paramsFormlet :: Maybe Params -> Form s m Params
-- Same as: paramsFormlet :: Formlet s m Params
paramsFormlet mparams = fieldsToTable $ Params
  <$> intField "Minimum number" (fmap minNumber mparams)
  <*> intField "Maximum number" (fmap maxNumber mparams)
  <*> stringField "Single word" (fmap singleWord mparams)
  <*> stringField "Plural word" (fmap pluralWord mparams)
  <*> fileField  "test"

getRootR, postRootR :: GHandler Test Test RepHtml
getRootR = postRootR
postRootR = do
  (res,w,enc,nonce) <- runFormPost $ paramsFormlet Nothing
  defaultLayout $ do
    [$hamlet|
%form!enctype=$enc$
  $nonce$
  $show res$
  %table
    ^w^
    %tr
      %td!colspan=2
        %input!type=submit
|]

mkYesod "Test" [$parseRoutes|
/ RootR GET POST
|]

instance Yesod Test where approot _ = ""

main = basicHandler 3000 Test