> in case you're doing so this way:
> ocamlc -o my.cma mod1.ml mod2.ml mod3.ml mod4.ml
> 
> this will recompile everything,
> but you can use in your makefile:
> (...)
> then you don't recompile everything, only the modified module
> 

Yes, with ocamlbuild I need not to recompile everything, but it's slow 
traversing even nothing-to-be-done tree:

Finished, 432 targets (411 cached) in 00:00:08.

It takes already 8 seconds if nothing is touched.

If I edit few files, it's worse:

Finished, 432 targets (256 cached) in 00:00:49.

I'm looking for alternatives.

That's why I try with scripting: keep core libraries compiled and run 
outermost parts with an interpreter.

Another idea is to change ocamlbuild to work dynamically: keep the 
dependency tree in memory and update it from time to time, watching 
files on disk.

Dawid