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json parser
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import System.Environment | |
import Control.Applicative((<|>)) | |
import Data.Char | |
( isAscii | |
, isDigit | |
) | |
import Data.Map | |
import Text.ParserCombinators.ReadP | |
data JsonValue = | |
JsonNumber Double | |
| JsonString String | |
| JsonBool Bool | |
| JsonNull | |
| JsonArray [JsonValue] | |
| JsonObject (Map String JsonValue) | |
deriving Show | |
jsonNumber :: ReadP JsonValue | |
jsonNumber = jsonDouble <|> jsonInteger | |
jsonDouble :: ReadP JsonValue | |
jsonDouble = do | |
num <- many1 (satisfy isDigit) | |
dot <- char '.' | |
num1 <- many1 (satisfy isDigit) | |
return $ JsonNumber (read (num ++ [dot] ++ num1)) | |
jsonInteger :: ReadP JsonValue | |
jsonInteger = do | |
num <- many1 (satisfy isDigit) | |
return $ JsonNumber (read num) | |
jsonNull :: ReadP JsonValue | |
jsonNull = do | |
string "null" | |
return JsonNull | |
jsonString :: ReadP JsonValue | |
jsonString = do | |
char '"' | |
key <- many $ satisfy (\c -> c /= '"') | |
char '"' | |
return $ JsonString key | |
jsonTrue :: ReadP JsonValue | |
jsonTrue = do | |
string "true" | |
return $ JsonBool True | |
jsonFalse :: ReadP JsonValue | |
jsonFalse = do | |
string "false" | |
return $ JsonBool False | |
jsonBool :: ReadP JsonValue | |
jsonBool = jsonTrue <|> jsonFalse | |
jsonArray :: ReadP JsonValue | |
jsonArray = do | |
char '[' | |
skipSpaces | |
values <- sepBy jsonValue (skipSpaces *> char ',' <* skipSpaces) | |
skipSpaces | |
char ']' | |
return $ JsonArray values | |
jsonValue :: ReadP JsonValue | |
jsonValue = | |
skipSpaces *> | |
jsonNumber <|> jsonString <|> jsonNull <|> jsonObject <|> jsonBool <|> jsonArray | |
<* skipSpaces | |
jsonPair :: ReadP (String, JsonValue) | |
jsonPair = do | |
skipSpaces | |
(JsonString key) <- jsonString | |
skipSpaces | |
char ':' | |
skipSpaces | |
value <- jsonValue | |
return (key, value) | |
jsonObject :: ReadP JsonValue | |
jsonObject = do | |
char '{' | |
skipSpaces | |
pairs <- sepBy jsonPair (skipSpaces *> char ',' <* skipSpaces) | |
skipSpaces | |
char '}' | |
return $ JsonObject $ fromList pairs | |
parse :: String -> Maybe JsonValue | |
parse xs = if Prelude.null result | |
then Nothing | |
else resultOrFail result | |
where | |
result = readP_to_S (jsonObject <* skipSpaces) xs | |
resultOrFail :: [(JsonValue,String)] -> Maybe JsonValue | |
resultOrFail result = if Prelude.null $ snd $ last result | |
then Just $ fst $ last result | |
else Nothing | |
main :: IO () | |
main = do | |
(file:_) <- getArgs | |
contents <- readFile file | |
putStr contents | |
case parse contents of | |
(Just json) -> print json | |
Nothing -> putStrLn "invalid json" | |
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