Re: [Caml-list] ocambuild vs ocamldep circular dependencies

[Goswin von Brederlow <goswin-v-b@web.de>]

On Sat, Jul 09, 2016 at 09:45:46AM -0400, Gabriel Scherer wrote:
> Hi Michael,
> 
> 
> > One can of cause discuss if it is good style to have circular dependencies
> > between module implementations. One can also discuss if it is the job of a
> > build tool to enforce such policies, or if a build tool should reduce the
> > set of valid programs.
> 
> 
> I think there is a misconception here. The behavior of the compiler in
> presence of such circular dependencies is undefined. The current
> implementation happens to allow them, but this does not mean that they are
> "valid programs".

I thought that only worked with hacks, turning of cross module
inlining to make it build at all.

> On Sat, Jul 9, 2016 at 8:53 AM, Soegtrop, Michael <
> michael.soegtrop@intel.com> wrote:
> 
> > Dear OCaml Users and Developers,
> >
> > It has been discussed a few times on the list, that ocambuild treats .mli
> > and .ml files as one regarding dependencies (unlike ocamldep), so that
> > projects which have dependencies of the type A.ml depends on B.mli and B.ml
> > depends on A.mli, cannot be built with ocamlbuild, although they can be
> > built by other means.
> >
> > One can of cause discuss if it is good style to have circular dependencies
> > between module implementations. One can also discuss if it is the job of a
> > build tool to enforce such policies, or if a build tool should reduce the
> > set of valid programs.
> >
> > Let me describe the issue which gives me headaches right now. I am working
> > on a tool doing certain analysis on C programs. In this tool I have a
> > module handling types and a module handling constant folding. Both have a
> > circular dependency in their implementation. Look e.g. at this case:
> >
> > sizeof(int[3*4])*2
> >
> > The type handling module needs to call the constant folding module to get
> > the value of 3*4. The constant folding module needs to call the type module
> > for handling the sizeof. There are no easy ways around the circular
> > dependency here. One way would be to have a mutable value field in my AST
> > and write the folded values to the AST while doing constant folding, so
> > that the type module can access the value when it needs it. I have my
> > doubts that this is nicer than living with the circular dependency. Anyway
> > I want to be able to decide this and not be forced to a solution by a build
> > tool. I think there are many cases, where two modules are just handling
> > different aspects of a common complex data structure (in this case a C AST)
> > and there is no natural ordering between them.

I don't think you have explored all the ways around the circular depends yet.

1) factor out the common parts into a 3rd module used by both
2) use recursive modules
3) lift the recursion (old style): pass a record of callbacks to one
   of the modules to replace the cyclic calls
4) lift the recursion (first class modules): pass one of the modules
   as argument to the other and open it locally

> > As a result I would recommend to support in ocamlbuild the same dependency
> > model as ocamldep has (things are fine as long as .mli files don’t have
> > circular dependencies).
> >
> > The only way I see right now to get my job done is to discard ocamlbuild
> > and use OcamlMakefile. Since I use menhir –infer, I first have to modify
> > OcamlMakefile to handle dependencies in way menhir can live with.
> >
> > Best regards,
> >
> > Michael
> >
> > Intel Deutschland GmbH
> > Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany
> > Tel: +49 89 99 8853-0, www.intel.de
> > Managing Directors: Christin Eisenschmid, Christian Lamprechter
> > Chairperson of the Supervisory Board: Nicole Lau
> > Registered Office: Munich
> > Commercial Register: Amtsgericht Muenchen HRB 186928
> >

MfG
	Goswin