import qualified Data.Vector  as Vector

instance ToJSON a => ToJSON (NonEmptyList a) where
    toEncoding (NonEmptyList x xs) = toEncoding (x:xs)
instance FromJSON a => FromJSON (NonEmptyList a) where
    parseJSON = withArray "NonEmptyList" $ \array ->
        maybe (fail "Unable to parse values") pure (parseValues array)
        where
            parseVec = sequence . Vector.toList . Vector.map fromJSON
            parseValues array = Vector.uncons array >>=
                \(head, tail) -> case (fromJSON head, parseVec tail) of
                    (Success x, Success xs) -> pure $ NonEmptyList x xs
                    _                       -> fail "Unable to parse values"

import           Data.Aeson.Encoding

import qualified Data.Vector         as Vector

import           Data.NonEmptyList

instance ToJSON a => ToJSON (NonEmptyList a) where
    toEncoding list =
        let (x, xs) = uncons list
            in toEncoding (x:xs)
instance FromJSON a => FromJSON (NonEmptyList a) where
    parseJSON = withArray "NonEmptyList" $ \array ->
        maybe (fail "Unable to parse values") pure (parseValues array)
        where
            parseVec = sequence . Vector.toList . Vector.map fromJSON
            parseValues array = Vector.uncons array >>=
                \(head, tail) -> case (fromJSON head, parseVec tail) of
                    (Success x, Success xs) -> fromList (x:xs)
                    _                       -> fail "Unable to parse values"