RE: [Sml-implementers] FLI

[Dave B. <da...@ta...>]

At 13:27 18/09/2001, Robert Harper wrote:
>3. Standardization of a foreign function interface.  I have not thought very
>much about this issue, but I can certainly see difficulties with
>compatibility not only across implementations (the various compilers out
>there), but also across platforms (primarily, Unix vs Windows).  Fundamental
>issues such as the semantics of "int" will arise, since implementations
>differ, even on the same hardware and software platform, and since external
>code will impose its own requirements.  The need for an FFI is largely
>pragmatic --- we cannot re-invent the world ourselves in our own way.
>However, as someone pointed out, buying into foreign code will certainly
>limit portability across platforms and quite possibly across
>implementations.

I think it's quite the reverse.  At present, it is virtually impossible to
write a portable library that interfaces to C.  With a standard FLI, it
will be possible.  Of course it will remain possible for people to write
non-portable code, but it will also be possible to write portable code. 

Platform differences are always present when writing libraries.  If one
platform uses 64-bit ints and another uses 16-bit ints, you either have to
ignore it (if it isn't relevant), accept it, or work your way around it.
That doesn't stop many libraries being useful on a wide variety of
platforms.  Portability is always a matter of "how many platforms" rather
than "all or none".

In any case, portability isn't always what you want.  If I write an library
for accessing the registry, the Unix users out there won't care.  Access to
platform-specific libraries is just as important as writing portable libraries.

Dave.