generic support for records

[paolino]

I've managed to get it via generics-sop, but I don't have much experience in this stuff.

data T a = T
    { field_reps   :: Int
    , field_what   :: Text
    , field_ignore :: Char
    , field_inside :: a
    }
    deriving (Show, Eq)

deriveGeneric ''T -- SOP

-- relies on unjsonDef for all fields
unjT :: (Typeable a, Unjson a) => UnjsonDef (T a)
unjT = gunjson
        do T.stripPrefix "field_"
        do [  "number of repetitions"
                , "string to repeat"
                , "char to ignore"
                , "inside the T"
                ] 
        do T

-- specify unjsonDef per field
unjUT :: (Typeable a, Unjson a) => UnjsonDef (T a)
unjUT = gunjsonU
        do T.stripPrefix "field_"
        do C "number of repetitions" unjsonDef
                :* C "string to repeat" 
                    do invmap T.reverse T.reverse unjsonDef
                :* C "char to ignore"   unjsonDef
                :* C "inside the T"     unjsonDef
                :* Nil
        do T



instance (Typeable a, Unjson a) => Unjson (T a)
    where unjsonDef = unjUT

testV = T 54 "mamma" 'a' (T 32 "piero" 'p' (128 :: Int))

roundTest :: forall a.  (Unjson a, Eq a) => a -> Bool
roundTest x =  (parse unjsonDef . traceShowId . unjsonToJSON unjsonDef) x == Result x []

If you think it can be good to have, I can file a MR