codec

Simple bidirectional serialization https://github.com/chpatrick/codec

Latest on Hackage:0.2.1

This package is not currently in any snapshots. If you're interested in using it, we recommend adding it to Stackage Nightly. Doing so will make builds more reliable, and allow stackage.org to host generated Haddocks.

BSD3 licensed by Patrick Chilton
Maintained by chpatrick@gmail.com

Codec Build Status Hackage

Codec makes it simple to write composable bidirectional serializers with a consistent interface.

Just define your data type normally:

data RecordB = RecordB
  { recordBString :: String
  , recordBDouble :: Double
  } deriving (Eq, Ord, Show)

and then associate each field with a codec using the =. operator:

recordBObjCodec :: JSONCodec RecordB
recordBObjCodec = asObject "RecordB" $
  RecordB
    <$> recordBString =. field "string"
    <*> recordBDouble =. field "double"

That's it! If you want, you can now define ToJSON and FromJSON instances, or just use it directly:

instance ToJSON RecordB where
  toJSON = toJSONCodec recordBObjCodec
  toEncoding = toEncodingCodec recordBObjCodec

instance FromJSON RecordB where
  parseJSON = parseJSONCodec recordBObjCodec

Support can be added for almost any serialization library, but aeson and binary support is included.

JSON example:

data RecordA = RecordA
  { recordAInt :: Int
  , recordANestedObj :: RecordB
  , recordANestedArr :: RecordB
  , recordANestedObjs :: [ RecordB ]
  } deriving (Eq, Ord, Show)

data RecordB = RecordB
  { recordBString :: String
  , recordBDouble :: Double
  } deriving (Eq, Ord, Show)

recordACodec :: JSONCodec RecordA
recordACodec = asObject "RecordA" $
  RecordA
    <$> recordAInt =. field "int"
    <*> recordANestedObj =. field' "nestedObj" recordBObjCodec
    <*> recordANestedArr =. field' "nestedArr" recordBArrCodec
    <*> recordANestedObjs =. field' "nestedObjs" (arrayOf' id id recordBObjCodec)

recordBObjCodec :: JSONCodec RecordB
recordBObjCodec = asObject "RecordB" $
  RecordB
    <$> recordBString =. field "string"
    <*> recordBDouble =. field "double"

-- serialize to array elements
recordBArrCodec :: JSONCodec RecordB
recordBArrCodec = asArray "RecordB" $
  RecordB
    <$> recordBString =. element
    <*> recordBDouble =. element

Binary example:

data RecordA = RecordA
  { recordAInt64 :: Int64
  , recordAWord8 :: Word8
  , recordANestedB :: RecordB
  } deriving (Eq, Ord, Show)

data RecordB = RecordB
  { recordBWord16 :: Word16
  , recordBByteString64 :: BS.ByteString
  } deriving (Eq, Ord, Show)

recordACodec :: BinaryCodec RecordA
recordACodec =
  RecordA
    <$> recordAInt64 =. int64le
    <*> recordAWord8 =. word8
    <*> recordANestedB =. recordBCodec

recordBCodec :: BinaryCodec RecordB
recordBCodec =
  RecordB
    <$> recordBWord16 =. word16host
    <*> recordBByteString64 =. byteString 64

A Codec is just a combination of a deserializer r a, and a serializer c -> w a.

data CodecFor r w c a = Codec
  { codecIn :: r a
  , codecOut :: c -> w a
  }
  
type Codec r w a = CodecFor r w a a

With binary for example, r is Get and w is PutM. The reason we have an extra parameter c is so that we can associate a Codec with a particular field using the =. operator:

(=.) :: (c' -> c) -> CodecFor r w c a -> CodecFor r w c' a

Codec is an instance of Functor, Applicative, Monad and Profunctor. You can serialize in any order you like, regardless of field order in the data type:

recordBCodecFlipped :: BinaryCodec RecordB
recordBCodecFlipped = do
  bs64 <- recordBByteString64 =. byteString 64
  RecordB
    <$> recordBWord16 =. word16host
    <*> pure bs64

Contributors

=. operator and Profunctor approach thanks to Xia Li-yao

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