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Date: Thu, 03 Oct 2013 19:45:07 +0200
From: Alain Frisch <alain@frisch.fr>
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Subject: Re: [Caml-list] empty mli for executable

On 10/03/2013 06:50 PM, Milan Stanojević wrote:
> ocaml compiler executables have empty mlis with the following comment
> (*
>    this "empty" file is here to speed up garbage collection in ocamlopt.opt
> *)
>
> Can someone explain this in more detail?
> How does empty interface lead to faster gc-ing?

The empty interface implies that toplevel values computed by those 
modules don't need to be stored in the global symbol slots.  Those slots 
are roots for the GC and are thus scanned every time it runs.  The fewer 
global symbols, the quicker the GC will be.  Well, this is the theory, 
I'd be really surprised if this materialized in a speed up  which can be 
observed.

Having an empty interface has a much more practical interest, in 
general: it allows the compiler to detect unused declarations in the 
implementation (if the corresponding warnings are enabled), and thus to 
reduce code rot.


-- Alain