Haskell Illegal deriving item Generic

-# LANGUAGE DataKinds #-
-# LANGUAGE DeriveGeneric #-
-# LANGUAGE OverloadedStrings #-
-# LANGUAGE TypeOperators #-

import qualified Data.ByteString.Lazy as BL
import Data.Csv (DefaultOrdered, FromRecord,
ToNamedRecord, ToRecord)
import Data.Generics
import Data.Proxy
import qualified Data.Text as T
import Network.HTTP.Client (newManager)
import Network.HTTP.Client.TLS (tlsManagerSettings)
import Servant.API
import Servant.Client
import Servant.CSV.Cassava
import System.Environment

data Cata = Cata

csvDate :: String,
csvOpen :: String,
csvHigh :: String,
csvLow :: String,
csvClose :: String,
csvVolume :: String,
csvExDividend :: String,
csvSplitRatio :: String,
csvAdjOpen :: String,
csvAdjHigh :: String,
csvAdjLow :: String,
csvAdjClose :: String,
csvAdjVolume :: String
deriving (Show, Generic)

instance DefaultOrdered Cata
instance FromRecord Cata
instance ToNamedRecord Cata
instance ToRecord Cata


I compile the above code and get the following error: why?

$ stack ghc servantcsv.hs
[1 of 1] Compiling Main ( servantcsv.hs, servantcsv.o )

servantcsv.hs:34:21: error:
• Illegal deriving item ‘Generic’
• In the data declaration for ‘Cata’
|
34 | } deriving (Show, Generic)
| ^^^^^^^


GHC Version: ghc-8.4.3

ghc-8.4.3

1 Answer
1

You want to import GHC.Generics not Data.Generics. What you have imported does have a type Generic but it isn't a class:

GHC.Generics

Data.Generics

Generic

type Generic c = forall a. Data a => a -> c a


Certainly that can't be part of a "deriving" clause.

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