Thoughts about how to build Argonaut Haskell Edition.

argonaut.hs

data Json = JsonBool Bool
          | JsonArray [Json]
          | JsonNull
          deriving (Eq, Show)

type JSONError = ()

type JSONReader a b = a -> Either JSONError (b, a)

boolReader :: (Bool -> b) -> JSONReader String b
boolReader transform ('t' : 'r' : 'u' : 'e' : tail) = Right (transform True, tail)
boolReader transform ('f' : 'a' : 'l' : 's' : 'e' : tail) = Right (transform False, tail)
boolReader _ _ = Left ()

arrayElementReader :: a -> (a -> b -> a) -> JSONReader String b -> JSONReader String a
arrayElementReader init fold elementReader (',' : tail)  = arrayElementReader init fold elementReader tail
arrayElementReader init _ _ (']' : tail)                 = Right (init, tail)
arrayElementReader init fold elementReader text          = case (elementReader text) of
                                                                                (Left error)          -> Left error
                                                                                (Right (elem, tail))  -> arrayElementReader (fold init elem) fold elementReader tail

arrayReader :: a -> (a -> b -> a) -> JSONReader String b -> JSONReader String a
arrayReader init fold elementReader ('[' : tail)  = arrayElementReader init fold elementReader tail
arrayReader _ _ _ _                               = Left ()

nullReader :: a -> JSONReader String a
nullReader value ('n' : 'u' : 'l' : 'l' : tail) = Right (value, tail)

jsonReader :: JSONReader String Json
jsonReader text@('t' : _) = boolReader JsonBool text
jsonReader text@('f' : _) = boolReader JsonBool text
jsonReader text@('n' : _) = nullReader JsonNull text
jsonReader text@('[' : _) = fmap (\(arr, tail) -> (JsonArray $ reverse arr, tail)) $ arrayReader [] (flip (:)) jsonReader text