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{-# LANGUAGE GADTs #-}
module GHC.Utils.Json where
import GHC.Prelude
import GHC.Utils.Outputable
import Data.Char
import Numeric
-- | Simple data type to represent JSON documents.
data JsonDoc where
JSNull :: JsonDoc
JSBool :: Bool -> JsonDoc
JSInt :: Int -> JsonDoc
JSString :: String -> JsonDoc
JSArray :: [JsonDoc] -> JsonDoc
JSObject :: [(String, JsonDoc)] -> JsonDoc
-- This is simple and slow as it is only used for error reporting
renderJSON :: JsonDoc -> SDoc
renderJSON d =
case d of
JSNull -> text "null"
JSBool b -> text $ if b then "true" else "false"
JSInt n -> ppr n
JSString s -> doubleQuotes $ text $ escapeJsonString s
JSArray as -> brackets $ pprList renderJSON as
JSObject fs -> braces $ pprList renderField fs
where
renderField :: (String, JsonDoc) -> SDoc
renderField (s, j) = doubleQuotes (text s) <> colon <+> renderJSON j
pprList pp xs = hcat (punctuate comma (map pp xs))
escapeJsonString :: String -> String
escapeJsonString = concatMap escapeChar
where
escapeChar '\b' = "\\b"
escapeChar '\f' = "\\f"
escapeChar '\n' = "\\n"
escapeChar '\r' = "\\r"
escapeChar '\t' = "\\t"
escapeChar '"' = "\\\""
escapeChar '\\' = "\\\\"
escapeChar c | isControl c || fromEnum c >= 0x7f = uni_esc c
escapeChar c = [c]
uni_esc c = "\\u" ++ (pad 4 (showHex (fromEnum c) ""))
pad n cs | len < n = replicate (n-len) '0' ++ cs
| otherwise = cs
where len = length cs
class ToJson a where
json :: a -> JsonDoc
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