Data.Aeson.Parser.Internal

Efficiently and correctly parse a JSON string. The string must be encoded as UTF-8.

Lazy parsers

json :: Parser Value

Parse any JSON value.

The conversion of a parsed value to a Haskell value is deferred until the Haskell value is needed. This may improve performance if only a subset of the results of conversions are needed, but at a cost in thunk allocation.

This function is an alias for value. In aeson 0.8 and earlier, it parsed only object or array types, in conformance with the now-obsolete RFC 4627.

Warning

If an object contains duplicate keys, only the first one will be kept. For a more flexible alternative, see jsonWith.

jsonEOF :: Parser Value

Parse a top-level JSON value followed by optional whitespace and end-of-input. See also: json.

jsonWith :: ([(Text, Value)] -> Either String Object) -> Parser Value

Parse any JSON value.

This parser is parameterized by a function to construct an Object from a raw list of key-value pairs, where duplicates are preserved. The pairs appear in reverse order from the source.

Examples

json keeps only the first occurence of each key, using fromList.

json = jsonWith (Right . fromList)

jsonLast keeps the last occurence of each key, using fromListWith (const id).

jsonLast = jsonWith (Right . fromListWith (const id))

jsonAccum keeps wraps all values in arrays to keep duplicates, using fromListAccum.

jsonAccum = jsonWith (Right . fromListAccum)

jsonNoDup fails if any object contains duplicate keys, using parseListNoDup.

jsonNoDup = jsonWith parseListNoDup

jsonLast :: Parser Value

Variant of json which keeps only the last occurence of every key.

jsonAccum :: Parser Value

Variant of json wrapping all object mappings in Array to preserve key-value pairs with the same keys.

jsonNoDup :: Parser Value

Variant of json which fails if any object contains duplicate keys.

value :: Parser Value

Parse any JSON value. Synonym of json.

jstring :: Parser Text

Parse a quoted JSON string.

jstring_ :: Parser Text

Parse a string without a leading quote.

scientific :: Parser Scientific

Parse a JSON number.

Strict parsers

json' :: Parser Value

Parse any JSON value.

This is a strict version of json which avoids building up thunks during parsing; it performs all conversions immediately. Prefer this version if most of the JSON data needs to be accessed.

This function is an alias for value'. In aeson 0.8 and earlier, it parsed only object or array types, in conformance with the now-obsolete RFC 4627.

Warning

If an object contains duplicate keys, only the first one will be kept. For a more flexible alternative, see jsonWith'.

jsonEOF' :: Parser Value

Parse a top-level JSON value followed by optional whitespace and end-of-input. See also: json'.

jsonWith' :: ([(Text, Value)] -> Either String Object) -> Parser Value

Strict version of jsonWith.

jsonLast' :: Parser Value

Variant of json' which keeps only the last occurence of every key.

jsonAccum' :: Parser Value

Variant of json' wrapping all object mappings in Array to preserve key-value pairs with the same keys.

jsonNoDup' :: Parser Value

Variant of json' which fails if any object contains duplicate keys.

value' :: Parser Value

Strict version of value. Synonym of json'.

Helpers

decodeWith :: Parser Value -> (Value -> Result a) -> ByteString -> Maybe a

decodeStrictWith :: Parser Value -> (Value -> Result a) -> ByteString -> Maybe a

eitherDecodeWith :: Parser Value -> (Value -> IResult a) -> ByteString -> Either (JSONPath, String) a

eitherDecodeStrictWith :: Parser Value -> (Value -> IResult a) -> ByteString -> Either (JSONPath, String) a

Handling objects with duplicate keys

fromListAccum :: [(Text, Value)] -> Object

fromListAccum kvs is an object mapping keys to arrays containing all associated values from the original list kvs.

>>> fromListAccum [("apple", Bool True), ("apple", Bool False), ("orange", Bool False)]
fromList [("apple", [Bool False, Bool True]), ("orange", [Bool False])]

parseListNoDup :: [(Text, Value)] -> Either String Object

fromListNoDup kvs fails if kvs contains duplicate keys.