[MLton-user] FFI questions

[Matthew Fluet]

> Are there MLton types matching long and size_t?  Currently, it seems
> that MLton is 32-bit only, but this might change in the future.  So
> using Int32 and Word32 seems unwise.

Using Int<N> and Word<N> is currently your best (and only) option.  The
number of bits used to represent a C long and a C size_t is platform
dependent, so you'll need to determine the right number of bits for your 
platform and using the corresponding Int/Word structure.

In the future, I think the right design will be to introduce a new ML 
Basis System library for FFI related structures.  I believe that we will 
be able to set up this library so that it provides something like:

 signature CTYPES =
   struct
     SChar : INTEGER
     UChar : WORD
     SInt : INTEGER
     UInt : WORD
     SLong : INTEGER
     ULong : WORD
     SLongLong : INTEGER
     ULongLong : WORD
     SizeT : WORD
     ...
   end

and these would be bound to appropriate Int<N>/Word<N> structures 
depending upon the target platform. 

> I'm interfacing a library which stores pointers to char arrays, and
> it's the task of the application to ensure that the arrays are not
> freed while the library is still using them.  Is there an easy way to
> prevent MLton from freeing a string?  Or should I use malloc and
> memcpy, and manage memory by hand?

There is currently no way to pin ML objects with the current version of 
MLton; so your only immediate option will be to manage the memory by hand.

On the MLton development list, there has been a recent discussion on how 
to provide this functionality:

  http://mlton.org/pipermail/mlton/2005-July/027461.html

However, nothing has been implemented yet.