Reading/Writing Binary Data in Haskell

[Glynn Clements]

Gordon James Miller wrote:

> 1 - Is there yet a standard, or at least commonly supported by hugs and 
> ghc, method for dealing with binary data.
> 
> 2 - If not, is there a "standard" library that is used to manipulate 
> binary data.  I've seen some references to some implementations but 
> given that this is being done in my limited spare time (I'm not a full 
> time student) I'd rather not spin my wheels on something that's going 
> to be dead in a matter of months.

There isn't a standard mechanism for binary I/O.

However, a simple and fairly generic mechanism for doing this is:

1. Read in a list of "Char"s with the standard I/O functions.
2. Use "map (fromIntegral . ord) ..." to get a list of "Word8"s (octets).
3. Use with, poke, peek, castPtr etc to coerce a list of octets to the
desired type(s).

For output, do the reverse.

This way, you can read/write any instance of Storable in the host's
native format (i.e. "C" format), and the code should be portable.

The key here is step 3; if you want to sacrifice portability for
performance, use Posix.read (or the Win32 equivalent) to read directly
into memory (Ptr/Addr), or even write an import declaration for
mmap().

-- 
Glynn Clements <glynn.clements@virgin.net>