Blank page with applicativeDo

[cdupont]

reform-blaze doesn't seem to play well with applicativeDo (from GHC 8). Just adding {-# LANGUAGE ApplicativeDo #-} to a code containing reform forms makes the happstack server to return a blank page.

[cdupont]

@stepcut Any idea?

[stepcut]

I can not duplicate this error. This is my current test code:

{-# language OverloadedStrings #-}
{-# language TypeFamilies #-}
{-# language ApplicativeDo #-}
module Main where

import Data.Text (Text)
import Text.Blaze.Html
import qualified Text.Blaze.Html5 as H
import Happstack.Server
import Text.Reform
import Text.Reform.Happstack
import Text.Reform.Blaze.Text

instance FormError AppError where
    type ErrorInputType AppError = [Input]
    commonFormError = AppCFE

data AppError = AppCFE  (CommonFormError [Input])

type SimpleForm = Form (ServerPartT IO) [Input] AppError Html ()

postForm :: SimpleForm Text
postForm =
  label ("Any text value: " :: Text) ++> inputText "" <* inputSubmit "submit"

route =
  do decodeBody (defaultBodyPolicy "/tmp/" 0 1000 1000)
     html <- reform (form ("/" :: Text)) "post" success Nothing postForm
     ok $ toResponse $ appTemplate "form" $ html
     where
       success :: Text -> ServerPartT IO Response
       success msg =
         ok $ toResponse $ appTemplate "Success" (H.p (toHtml msg))

appTemplate ttl bdy =
  do H.html $
      do H.head $ H.title ttl
         H.body bdy

main = simpleHTTP nullConf route

[stepcut]

One thing you could try is using the bifunctors branch of reform:

https://github.com/Happstack/reform/tree/bifunctors

This switches from the local IndexedApplicative to Bifunctors and removes the bogus Monad Result instance. Despite those big sounding changes, all my code compiled with out changes.