[Haskell-cafe] Linking and unsafePerformIO

[Alexander Dunlap]

On Tue, Oct 14, 2008 at 2:14 PM, Jules Bean <jules at jellybean.co.uk> wrote:
> David Roundy wrote:
>>
>> On Tue, Oct 14, 2008 at 05:20:35PM +0100, Jules Bean wrote:
>>>
>>> Running a program on a different interpreter or compiler had better
>>> not change its denotation, otherwise it [the denotation] is not much
>>> use as a basis for reasoning.
>>
>> But you're saying above that we can't change programs, right? You
>> probably won't be surprised to hear that different compilers are
>> different programs.  And different packages are also different
>> programs.  Are you the only one who's allowed to fix bugs?
>
> No. I think we must be at cross purposes.
>
> I'm saying that we can change programs, and that changes their denotation,
> and that's fine, and anyone can do that. But the denotation of a program is
> supposed to be something independent of a particular compiler or OS or MAC
> address or RAM size or any of the millions of other things which probably
> don't change during the single run of a program.
>
> Putting these things into the IO monad is not an abuse of the IO monad. It
> is simply an acknowledgement that they are runtime things, and not
> denotational constructs.
>
>
> Jules
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But they aren't runtime constructs, they are compile-time constructs,
just like how (+) has a different meaning when you are on Windows than
it does when you are on Linux: they have different ways of allocating
memory, adding two numbers, putting the result somewhere, etc. Really,
they still denote the same thing ("add two numbers"), they just
abstract over system-dependent details.

Alex