There are a number of binary I/O libraries available for Haskell. The best to use is the new, semi-standard Data.Binary library:
It's very simple to use, and provides a highly efficient, pure interface to binary serialisation.
For just writing binary data to file, use
It is a part of the base package, so it comes with GHC.
See also Dealing with binary data
2 Other libraries
- JeremyShaw's update of HalDaume's NewBinary package (Cabalized): http://www.n-heptane.com/nhlab/repos/NewBinary
- Data.ByteString (Cabalised) also provides byte level operations, and is used in some applications for binary IO
- SerTH, the TH version (sort of) of NewBinary.
- PeterSimons's BlockIO package (Cabalized): http://cryp.to/blockio/
- JohnGoerzen's MissingH package (Cabalized): http://quux.org/devel/missingh
- SimonMarlow's experimental NewIO package: http://www.haskell.org/~simonmar/new-io.tar.gz (documentation at http://www.haskell.org/~simonmar/io/)
If you have simple binary IO requirements, then Data.ByteString might be easiest -- you get a List-like interface to packed byte arrays (interface documented here). For more complex serialisation, Data.Binary would be preferred.