[Haskell-cafe] Re: Linking and unsafePerformIO

Mauricio briqueabraque at yahoo.com
Tue Oct 14 09:58:24 EDT 2008

>> Hi,
>> If I have a Haskell wrapper (with unsafe...)
>> over a function that's never going to return
>> different values and is always side-effect
>> free, but can change depending on compile time
>> options of its library; my program is running,
>> and then the version of my library is updated
>> by my distribution smart instalation system,
>> which does update versions of libraries in
>> use; is it possible that I get a wrong behavior
>> of my program?
>> I do not understand enough about package
>> management to understand how running programs
>> or libraries are updated, and less about how
>> linking works between Haskelll and libraries
>> on other languages, so I don't know if my
>> program is guaranteed to stay with a single
>> version of a library for each run.
>> (Sure this is a weird situation, but I do
>> like to think about worst cases.)
> In practice that is fine, with current RTSes and so on.
> In principle it's not fine. A 'constant' should be constant over all 
> time, not just constant over a particular library version or sub-version 
> or a particular program invocation or OS or....
> Who knows, maybe some future haskell runtime will be able to perform the 
> trickery you describe and will cause this to break ;)

What I actually want to use that way are build
time configs. For instance, 'isThisLibraryThreadSafe'
or 'maximumNumberOfBigObjects'. Actually, I don't
know why people allow build time options at all.
We always use the "best set of options", and the
alternatives are there just to compel us to check
for them :)


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