[ OK, Mr. Low-Level takes the chance to re-present his little hTell
proposal here... ]
I suggest considering the following as a typo/blunder in the Haskell 98
report, for the same reasons as for the changes to the Directory library.
Here it goes:
There are a few design flaws regarding the file positioning functions
in the IO library:
* Why are there *two* ways to reposition a handle (one via hSeek
and the other one via hSetPosn)?
* Why is the handle supposed to be contained in HandlePosn? This
way one can't keep "a finger" within a file without keeping
it open. One has to be careful because the file can change in
the meantime, but this is not under Haskell's control, anyway.
* If we have a hSeek, where is hTell?
Fixing these points can be done quite easily without breaking any
existing code (with the exception that a new constructor and a new
function are visible now):
1) Make HandlePosn non-opaque and export it that way:
data HandlePosn = HandlePosn Handle Integer deriving (Eq,Show)
2) Add and export
hTell :: Handle -> IO Integer
with the "obvious" semantics, see e.g. "man ftell". :-)
3) For backwards compatibility keep hGetPosn/hSetPosn, but define
them via hTell/hSeek:
hGetPosn :: Handle -> IO HandlePosn
hGetPosn h = hTell h >>= \p -> return (HandlePosn h p)
hSetPosn :: HandlePosn -> IO ()
hSetPosn (HandlePosn h p) = hSeek h AbsoluteSeek p
Those functions should be removed for H2K.
4) Perhaps add
typedef HandlePosition = Integer
and use it in the code above, but I've got no strong opinion
about this.
Rationale: Keeping a file position opaque is a bad idea, because
*lots* of file formats rely on the fact that arithmetic is possible
on file positions, see e.g. http://www.wotsit.org/. Merging a file
position with a handle is even worse, because this keeps the file
open even when only the position is needed later.
And a last remark about arithmetic on file positions, as pointed
out by Fergus(Hender)son: One has to be careful about CR/LF vs LF,
but this is not a problem in the real world, ZIP works on M$, too!
:-)
This is all very low-level stuff, but real programs have to deal
with real file formats and the current IO lib makes things extremely
ugly. And another suggestion: Standardize the Socket library in some
way, all sensible operating systems have sockets by now (or the OS
will vanish soon, anyway, due to the omnipresent internetworking).
Hava a look at Java: Even Joe Programmer can write networking code
with a few lines there.
Cheers,
Sven
--
Sven Panne Tel.: +49/89/2178-2235
LMU, Institut fuer Informatik FAX : +49/89/2178-2211
LFE Programmier- und Modellierungssprachen Oettingenstr. 67
mailto:[EMAIL PROTECTED] D-80538 Muenchen
http://www.informatik.uni-muenchen.de/~Sven.Panne
