Return JSON from yesod handler

Question

I'm trying to write a simplest JSON response from Yesod's handler, but have some really stupid error (apparently). My handler code is this:

-- HelloYesod/Handler/Echo.hs
module Handler.Echo where

import           Data.Aeson      (object, (.=))
import qualified Data.Aeson      as J
import           Data.Text       (pack)
import           Import
import           Yesod.Core.Json (returnJson)

getEchoR :: String -> Handler RepJson
getEchoR theText = do
  let json = object $ ["data" .= "val"]
  return json

Error is this:

Handler/Echo.hs:12:10:
    Couldn't match expected type `RepJson' with actual type `Value'
    In the first argument of `return', namely `json'
    In a stmt of a 'do' block: return json
    In the expression:
      do { let json = object $ ...;
           return json }
Build failure, pausing...

Answer 1

I got caught by this one too: you just have to change your type signature and it will work:

getEchoR :: String -> Handler Value

My understanding is that the whole Rep system is deprecated in Yesod 1.2, so Handler's now return Html and Value rather than RepHtml and RepJson.

Hope this helps!