xcodec: Classes for working with generically typed codecs.

xcodec

The XCodec Haskell library provides a type-class for generic programming on bit data for writing encoders and decoders for codecs. The BinaryTranscoder class provides a common interface of methods for processing binary data, and default instances for the bytestring types: ByteString, ShortByteString, and LazyByteString. The StreamTranscoder class then provides the abstract methods for a generic function encoding from and a generic function decoding to the types implementing BinaryTranscoder.

Why?

XCodec exists to abstract common patterns that arise when writting code with the bytestring library in Haskell:

• Reusing code for ShortByteString, ByteString and LazyByteString.
• Having common interface for transfering into the bytestring Builder type.
• Reading to and from numeric values for bitwise manipulation or initializing from constant values.

Making bytestring code generic, can also make code more memory efficient; for example, we can write functions for BinaryTranscoder and apply them to LazyByteString when reading large files and to ShortByteString when working on smaller internal structures.

Examples

Using XCodec we can easily read numeric bit data to binary formats, programmatically:

import Data.ByteString (ByteString)
import Data.ByteString.Short (ShortByteString)
import Data.ByteString.Lazy (LazyByteString)
import Data.Word (Word16)
import Data.XCodec.BinaryTranscoder (packValue)

-- Infers: packValue :: Int -> ByteString
exStrict :: ByteString
exStrict = packValue (0xdeadbeef :: Int)

-- Infers: packValue :: Integer -> LazyByteString
exLazy :: LazyByteString
exLazy = packValue (0xf000000000000000000000000000000000000000000d :: Integer)

-- Infers: packValue :: Word16 -> ShortByteString
exShort :: ShortByteString
exShort = packValue (0xcafe :: Word16)

And then serialize them through a common interface:

import Data.ByteString.Builder (toLazyByteString, string8)
import Data.XCodec.BinaryTranscoder (serializeValue)

deadbeefThreeTimes :: LazyByteString
deadbeefThreeTimes =
  toLazyByteString . mconcat $
    [ serializeValue exLazy,
      serializeValue exStrict,
      serializeValue exShort,
      string8 "Hello, World!"
    ]

It also enables extracting binary data into Integer format so that bitwise transformations can be performed on large sets of binary data in O(n) time:

import Data.Bits ((.<<.), (.&.))
import Data.Word (Word8)
import Data.XCodec.BinaryTranscoder (unpackValue)

-- Extracts the byte at the bit number (LSB=0).
byteWindowAt :: (BinaryTranscoder bxc) => bxc -> Int -> Word8
byteWindowAt bxc idx = fromIntegral $ (unpackValue bxc .>>. idx) .&. 0xFF

Licensing

The xcodec project and its modules are free software and licensed under the BSD 3-clause license. See LICENSE.txt.

Copyright © 2026 Zoey McBride | zoeymcbride@mailbox.org