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From: Goswin von Brederlow <goswin-v-b@web.de>
To: Alexy Khrabrov <deliverable@gmail.com>
Cc: caml-list <caml-list@inria.fr>
References: <4D64C4F9-251E-4E76-8269-361C444E8F8F@gmail.com>
Date: Fri, 15 Apr 2011 10:37:42 +0200
In-Reply-To: <4D64C4F9-251E-4E76-8269-361C444E8F8F@gmail.com> (Alexy
	Khrabrov's message of "Thu, 14 Apr 2011 19:32:16 -0400")
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Subject: Re: [Caml-list] swapping variant modules via subdirectories fails at link time

Alexy Khrabrov <deliverable@gmail.com> writes:

> I have a module a.ml, containing some functions I want to alter in a version of my program.  I'd like to do it on the command line at link time, to obtain either the original, or an altered version.  
>
> Here's the original make line, simplified:
>
> %.cmx: %.ml
> 	ocamlfind ocamlopt $(DEBUG) $(OPTFLAGS) -package $(PACKAGES) -c $^ -o $@
>
> prog.opt: lib.cmxa a.cmx x.cmx prog.ml
> 	ocamlfind ocamlopt $(DEBUG) $(OPTFLAGS) -package $(PACKAGES) -linkpkg $^ -o $@
>
> I tried to create the variant by placing an altered version of a.ml in a subdirectory, var/, and linking that:
>
> prog.var.opt: lib.cmxa var/a.cmx x.cmx prog.ml
> 	ocamlfind ocamlopt $(DEBUG) $(OPTFLAGS) -package $(PACKAGES) -linkpkg $^ -o $@
>
> Further, I've created a.mli at the root level, and compiled it with
>
> ocamlfind ocamlc a.mli
>
> -- it needs lib.cmo to work, a byte-code version of lib.cmxa, which I make first.
>
> With that a.cmi at the root level, I can remake prog.opt fine.  If I copy or symlink a.cmi to var/, or symlink a.mli there, and try to make prog.var.opt, I get an error at prog.ml that files var/a.cmx and x.cmx make inconsistent assumptions about the interface A.
>
> The var/a.cmx is made by the same above pattern rule as ./a.cmx.  Even when ./a.cmi and var/a.cmi are the same, the same inconsistent error shows up!  Renaming ./a.ml out of the way and symlinking var/a.ml to ./ remakes prog.opt fine, which I can then rename prog.var.opt manually and hope to do it every time I need that, yet it's tiresome.   What prevents the original scheme from working?
>
> -- Alexy

You need to compile a.ml inside var/ instead of compiling var/a.ml.

MfG
        Goswin