[MLton-user] Conditional compilation

[Sean McLaughlin]

Hello,

   This is a feature request.  Or at least a request for a discussion.

   I have a fairly large (for a single person) software project that  
does a number of related tasks.  Many of these tasks are considerably  
improved by using external C packages for which I wrote ffi code.  Now  
that others are trying to compile the software, I have a problem.  If  
they don't have the relevant C library, for instance CPLEX, a  
proprietary linear programming solver, the code won't compile.  Now,  
the code using CPLEX may never be needed by a particular user, or they  
may be equally well served by using a free alternative such as GLPK,  
for which I also have ffi stubs.
   My current solution is to use #include a file that has the names of  
the relevant libraries, and each of my
mlb files are preprocessed using cpp to generate the actual mlb file  
that will be compiled.  This is a somewhat ugly solution.  If MLton  
supported some kind of preprocessing directives, as you do for the  
single variable SMLNJ_VERSION.  According to http://mlton.org/CompilationManager 
, no other symbols are defined.
If only I could define my own symbols, I'd be able to avoid the gcc  
step, which would be a considerable
improvement.  Would it be very difficult to allow a user to define his  
own preprocessing variables?

Thanks,

Sean