From: Christophe Raffalli <christophe.raffalli@univ-savoie.fr>

> Let say I want two distribute two(or more) implementations of a library
> with the .mli for all ...
> 
> Is there a way to choose the implementation at link time ?
> 
> Lets say I have a.mli compiled to a.cmi and a1.ml and a2.ml
> 
> I think (did not test) that putting the cmos in separate directory as
> a1/a.cmo and a2/a.cmo should allow the choice using the -I option ...
> 
> Any better solution (no dynlink, I want also native code) ?

Directories seem a possible solution.
Note that with native code you must be careful to compile without any
.cmx around (only .cmi's), as this would induce dependencies on a
specific version. This also means that you lose inlining (one major
advantage of native code.)

An alternative to distinct directories is to create libraries (.cma/.cmxa).
You could name them a1.cma and a2.cma, and link choosing either one.
Libraries are only used at link time, so their names are not
hard-coded. This solution has exactly the same pitfalls with native code.

Note that ocaml itself does something similar for vmthreads.
Distinct libraries for stdlib.cma and unix.cma are installed in a
distinct directory, but the .cmi's are not duplicated.
This library is bytecode only.

Jacques Garrigue