jsonparse.hs

module Parser where

data Token = Open_object | Close_object | Open_array | Close_array | List_delim |
             Assign_delim | Quote | String_literal String deriving (Show, Eq, Read)

data JsonElement = FullJsonArray [JsonElement] | StringValue String deriving (Show, Eq, Read)

tokens :: [(Char, Token)]
tokens = [
            ('{', Open_object),
            ('}', Close_object),
            ('[', Open_array),
            (']', Close_array),
            (',', List_delim),
            (':', Assign_delim),
            ('"', Quote)
         ]

token_list = map fst tokens

object_sample = "{\"var\": \"val\"}"
array_sample = "[\"x1\", \"x2\", [\"a1\"] ]"

tokenize :: String -> [Token]
tokenize "" = []
tokenize (' ' : rest) = tokenize rest
tokenize (a : rest) = let token = lookup a tokens 
                          predicate x = x /= '"' in
                        case token of
                        Nothing -> (String_literal $ takeWhile predicate (a:rest)) :
                                tokenize (dropWhile predicate (a:rest))
                        Just t -> t : tokenize rest

parse :: [Token] -> [JsonElement]
parse [] = []
parse (Quote : String_literal lit : Quote : List_delim : rest) = StringValue lit : parse rest
parse (Quote : String_literal lit : Quote : []) = [StringValue lit]
parse list | (head list == Open_array) || (last list == Close_array) =
            [FullJsonArray $ (parse . init . tail) list]

main = do
     print "hello json"
     print ((parse . tokenize) array_sample)