On the glasgow-haskell-users mailing list there's been a discussion on
file manipulation. Essentially several ghc users find the current
file-handling facilities inadequate.
Do any Haskell implementations support Binary files?
Have other Haskell users encountered difficulties handling files?
Theology:
I believe that Haskell's inadequate manipulation of files, or
persistent data, is a serious hinderance to it's use for real
applications. The perceived inadequacies of current functional file
manipulation are as follows:
1/ Using a printable representation, implies
o File must be reparsed on input
o data expansion
o loss of type information
o loss of sharing
2/ The file operations are monolithic: there are no facilities for
reading or writing a small part of a file.
3/ Hyperstrict read/write precludes the preservation of
o partially evaluated, and hence any potentially infinite, structures
o data structures containing functions.
4/ If the same file is read more than once and also written, the
file must logically be duplicated to preserve referential
transparency.
5/ There are some type issues, for example the contents of a binary
file must be dynamically typed, in contrast to the static typing
in the rest of the language.
Solutions:
There's no fundamental problem, it's just a matter of finding the
person-months to engineer a solution. Here are some thoughts on what a
solution should look like.
Orthogonal persistence is wonderful, but expensive and awkward in a
file-based environment. I believe we could get a long way with Binary
files, possibly with indexed-sequential access. A proposal on these
lines, together with a critique of existing file handling is in the
1992 Glasgow FP Workshop.
For anyone thinking of implementing Binary files, the Parallel Haskell
packing code that Will gave pointers to would be a good starting
place. It'd need to be simplified (it ensures the uniqueness of
closures on a processor). I'd be happy to discuss this any Brave Soul
who does the implementation. There are papers describing the
packing/unpacking in IFL 1995, and PLDI 1996.
Phil
