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.

 

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