Now I fixed it in a slightly different way: {-# LANGUAGE FlexibleContexts, FlexibleInstances, TypeFamilies, OverloadedStrings #-} module Main where import Control.Applicative import Control.Applicative.Indexed import Control.Monad import qualified Data.ByteString.Char8 as C import Text.Blaze import Text.Blaze.Html import qualified Text.Blaze.Html5 as H import qualified Text.Blaze.Html5.Attributes as A import Text.Blaze.Renderer.Utf8 (renderHtml) import Text.Reform import Text.Reform.Blaze.Common import Text.Reform.Happstack import Happstack.Server import SharedForm instance ToMarkup (DemoFormError [Input]) where toMarkup InvalidEmail = "Email address must contain a @." toMarkup InvalidUsername = "Username must not be blank." toMarkup (CommonError (InputMissing fid)) = H.toHtml $ "Internal Error. Input missing: " ++ show fid toMarkup (CommonError (NoStringFound input)) = H.toHtml $ "Internal Error. Could not extract a String from: " ++ show input toMarkup (CommonError (MultiStringsFound input)) = H.toHtml $ "Internal Error. Found more than one String in: " ++ show input usernameForm :: (Monad m, FormInput input, ToMarkup (DemoFormError input)) => String -> Form m input (DemoFormError input) Html () Username usernameForm initialValue = Username <$> *inputText initialValue* emailForm :: (Monad m, FormInput input, ToMarkup (DemoFormError input)) => String -> Form m input (DemoFormError input) Html ValidEmail Email emailForm initialValue = errorList ++> (label "email: " ++> (Email <<$>> *inputText initialValue* `prove` (validEmailProof InvalidEmail))) and got something even stranger: Taser.hs:32:18: Couldn't match expected type `Form m input (DemoFormError input) Html () String' with actual type `text0 -> Form m0 input0 error0 Html () text0' In the return type of a call of `inputText' Probable cause: `inputText' is applied to too few arguments In the second argument of `(<$>)', namely `inputText initialValue' In the expression: Username <$> inputText initialValue Taser.hs:38:56: Couldn't match expected type `Form m input (DemoFormError input) Html q0 a0' with actual type `text0 -> Form m0 input0 error0 Html () text0' In the return type of a call of `inputText' Probable cause: `inputText' is applied to too few arguments In the first argument of `prove', namely `inputText initialValue' In the second argument of `(<<$>>)', namely `inputText initialValue `prove` (validEmailProof InvalidEmail)' Please would somebody explain what's going on? Adrian. On 15 June 2013 17:19, Adrian May wrote:

Hi All,

I'm trying to get this example working:

http://patch-tag.com/r/stepcut/reform/snapshot/current/content/pretty/exampl...

It emitted what I took to be bitrot about ToHtml having apparently been generallised to ToMarkup and similar stuff, so I banged it into this form:

{-# LANGUAGE FlexibleContexts, FlexibleInstances, TypeFamilies, OverloadedStrings #-} module Main where

import Control.Applicative.Indexed import Control.Monad import qualified Data.ByteString.Char8 as C * import Text.Blaze * import qualified Text.Blaze.Html5 as H import qualified Text.Blaze.Html5.Attributes as A import Text.Blaze.Renderer.Utf8 (renderHtml) import Text.Reform * --import Text.Reform.Blaze.Common* * --import Text.Reform.Blaze.Text* * import Text.Reform.Blaze.String* import Text.Reform.Happstack import Happstack.Server import SharedForm

instance *ToMarkup* (DemoFormError [Input]) where *toMarkup* InvalidEmail = "Email address must contain a @." *toMarkup* InvalidUsername = "Username must not be blank." *toMarkup* (CommonError (InputMissing fid)) = H.toHtml $ "Internal Error. Input missing: " ++ show fid *toMarkup* (CommonError (NoStringFound input)) = H.toHtml $ "Internal Error. Could not extract a String from: " ++ show input *toMarkup* (CommonError (MultiStringsFound input)) = H.toHtml $ "Internal Error. Found more than one String in: " ++ show input

usernameForm :: (Monad m, FormInput input, *ToMarkup* (DemoFormError input)) => String -> Form m input (DemoFormError input) *Markup* NotNull Username usernameForm initialValue = ( *label "username: " ++>* (Username <<$>> inputText initialValue `prove` (notNullProof InvalidUsername))) {- usernameForm :: (Monad m, FormInput input, ToMarkup (DemoFormError input)) => String -> Form m input (DemoFormError input) Markup NotNull Username usernameForm initialValue = errorList ++> (*label "username: " ++> *(Username <<$>> inputText initialValue `prove` (notNullProof InvalidUsername))) -} blazeResponse :: *Markup* -> Response blazeResponse html = toResponseBS (C.pack "text/html;charset=UTF-8") $ renderHtml html

blazeForm :: *Markup* -> *Markup* blazeForm html = H.form ! A.action "/" ! A.method "POST" ! A.enctype "multipart/form-data" $ do html H.input ! A.type_ "submit"

formHandler :: (*ToMarkup* error, Show a) => Form (ServerPartT IO) [Input] error *Markup* proof a -> ServerPart Response formHandler form = msum [ do method GET html <- viewForm "user" form ok $ blazeResponse $ blazeForm html

, do method POST r <- eitherForm environment "user" form case r of (Right a) -> ok $ toResponse $ show a (Left view) -> ok $ blazeResponse $ blazeForm view

]

main :: IO () main = do let form = usernameForm "" simpleHTTP nullConf $ do decodeBody (defaultBodyPolicy "/tmp" 0 10000 10000) formHandler form

where *italics* indicate the bits I changed, but now I'm stumped by the * bold* bit barfing with:

Taser.hs:30:13: Ambiguous type variable `children0' in the constraints: (Data.String.IsString children0) arising from the literal `"username: "' at Taser.hs:30:13-24 (ToMarkup children0) arising from a use of `label' at Taser.hs:30:7-11 Probable fix: add a type signature that fixes these type variable(s) In the first argument of `label', namely `"username: "' In the first argument of `(++>)', namely `label "username: "' In the expression: (label "username: " ++> (Username <<$>> inputText initialValue `prove` (notNullProof InvalidUsername)))

If I take out label "username: " ++>, then it all works fine, except I don't have a label. I also tried putting the label inside the Username constructor with the same result.

I have the following versions installed:

* blaze-markup (library) Versions installed: 0.5.1.5 * blaze-html (library) Versions installed: 0.6.1.1 * reform (library) Versions installed: 0.1.2 * reform-blaze (library) Versions installed: 0.1.2 The Glorious Glasgow Haskell Compilation System, version 7.4.2

Perhaps the markup thing is what broke it, but I can't see ToHtml in any of those modules.

Thanks in advance, Adrian.