[Haskell-cafe] OS Abstraction module??

[Galchin Vasili]

yep .... FFI

On 10/22/07, Neil Mitchell <ndmitchell at gmail.com> wrote:
>
> Hi Bill,
>
> > > >     I am really talking about a module or perhaps a Haskell class
> that
> > > > provides notion for multiple threads of execution, semaphores, ..
> that
> > > > "hides" POSIX vs Win32 APIs .. i.e. the underlying OS APIs would be
> > totally
> > > > hidden.
> > >
> > > I think you are thinking in a "C" way. In Haskell, portable is the
> > > default. If you want to stop your code being portable, you have to go
> >
> >
> >      ^^ how? If I define something like "class OS where ...." and define
> a
> > POSIX instance of "class OS" and a Win32 API instance.. function calls
> will
> > be to the instances and hence the OS APIs are visible. Yes?
>
> OK, I think I'm slowly figuring out what you are meaning. You want to
> write some code which runs on POSIX, and some which runs on Win32,
> each of which bind to some foreign library which is different on both
> operating systems.
>
> The key thing to note about this is that whether a program is running
> on Windows or Posix is fixed at compile time. Things like classes can
> do some of what you seem to be after, but it tends to be easier to
> reach for the C pre processor.
>
> Let's take a simple login scenario. In Linux you enter the user name
> using the call getLine, and in Windows you call something else like
> getInputString. The way I would structure this would be:
>
> getUserName :: IO String
> #ifdef WINDOWS
> getUserName = getInputString
> #else
> getUserName = getLine
> #endif
>
> (Note - it wouldn't be WINDOWS - I can't remember what the blessed CPP
> for distinguishing Windows and Posix is)
>
> Then your logic code can call getUserName, and the platform
> differences are papered over.
>
> You could use classes, but for something which is OS dependent, I'd
> tend to use the CPP.
>
> Thanks
>
> Neil
>
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