> I was trying to trace a code with some significant amount of
> select'ed fds. At some point, I faced the fact that I just
> have no way to "show" a descriptor value.

OK, if it's just for debugging, and only intended to run under Unix,
you could use the following:

     external int_of_filedesc: Unix.file_descr -> int = "%identity"

> I know almost nothing about win32, but I was very surprised
> to discover that win32 has functions, isomorphic to
> low-level unix calls. However, I suspect (I don't have win32
> headers to look in just now) that HANDLE is again a
> "typedef" of intteger.

Not really.  It's a typedef of void *.  Values of this type look like
small integers, but no guarantees of this kind are given in the Win32
specs.  Moreover, a Unix.file_descr under Windows is not a HANDLE, but
a pair of a HANDLE and a flag saying whether it's a socket or not.

See, we really need type abstraction to hide these details :-)  And
also to catch common errors like confusing the "fd" and "length"
parameters to the read() or write() functions (in C).

- Xavier Leroy
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