Before calling decode
in ghci, you need to do :set -XOverloadedStrings
, so the string literal is treated as a ByteString instead of a String. The pragma in the module only applies to the code in the module, not to what you do in ghci.
Couldn't match expected type 'Data.ByteString.Lazy.Internal.ByteString' with actual type '[Char]'
Question
I'm trying to get a simple Json parser up and running in my Haskell code, I came across Data.Aeson which seemed like a viable solution to my problem
I followed the example code on the page, and with some minor modifications, here's what I got:
{-#LANGUAGE OverloadedStrings #-}
import Data.Aeson
import Data.Text
import Control.Applicative
import Control.Monad
data Person =
Person { firstName :: Text
, lastName :: Text
, age :: Int
} deriving Show
instance FromJSON Person where
parseJSON (Object v) =
Person <$> v .: "f_name"
<*> v .: "l_name"
<*> v .: "age"
parseJSON _ = mzero
Running the following in GHCi causes the nasty message in the title to appear:
decode "{\"f_name\":\"Haskell\", \"l_name\":\"Curry\",\"age\":114}" :: Maybe Person
So, does anyone here have an idea what went wrong? I followed the example code almost exactly as it was written, so why is it that it fails?
Solution
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