The codec package

[Tags:bsd3, library, test]

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Versions 0.1, 0.1.1, 0.2, 0.2.1
Dependencies aeson (>=1.0.0.0), base (>=4.6 && <6), binary, binary-bits, bytestring, mtl, profunctors, template-haskell, text, transformers, unordered-containers, vector [details]
License BSD3
Author Patrick Chilton
Maintainer chpatrick@gmail.com
Category Data
Home page https://github.com/chpatrick/codec
Source repository head: git clone https://github.com/chpatrick/codec.git
Uploaded Fri Apr 21 18:46:02 UTC 2017 by PatrickChilton
Distributions NixOS:0.2.1
Downloads 428 total (17 in the last 30 days)
Votes
1 []
Status Docs available [build log]
Last success reported on 2017-04-21 [all 1 reports]
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Readme for codec

Readme for codec-0.2.1

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