Question

Let message/en.msg file like:

Category1: some text 1
Category2: some text 2
    ...
CategoryN: some text N

And let next valid code:

getHomeR :: Handler RepHtml
getHomeR = do

    (msg :: AppMessage -> Text) <- getMessageRender

    let list = T.concat $ map msg [MsgCategory1, MsgCategory7]

    defaultLayout $ do
        $(widgetFile "homepage") -- <p>List: #{list}

then, list contains MsgCategory1 and MsgCategory7 translations.

I want to do some like:

    let list = T.concat $ map msg [MsgCategory1 .. MsgCategory7]

but AppMessage is not Enum derived.

My another one alternative is not valid too (is not Read derived too)

    let list = T.concat $ map (\n -> msg $ read "MsgCategory" ++ show n) [1 .. 7]

In general, how to cast “in real time” AppMessage elements?

Thank you very much!

(I love Yesod! 🙂 )

Answer 1

One way I found is here

deriving instance Enum AppMessage
deriving instance Eq AppMessage
deriving instance Read AppMessage
deriving instance Show AppMessage
...

(require -XStandaloneDeriving)

Explained:

Change on Foundation.hs:

-- Set up i18n messages. See the message folder.
mkMessage "App" "messages" "en"

-- Require extension: StandaloneDeriving
deriving instance Enum AppMessage

On site.cabal:

extensions: TemplateHaskell
            QuasiQuotes
            OverloadedStrings
            NoImplicitPrelude
            CPP
            MultiParamTypeClasses
            TypeFamilies
            GADTs
            GeneralizedNewtypeDeriving
            FlexibleContexts
            EmptyDataDecls
            NoMonomorphismRestriction
            StandaloneDeriving