[Omake] Type dependencies

[Aleksey Nogin]

On 13.03.2006 10:27, Jason Hickey wrote:

> While looking into this smarter command-line parsing, I ran into the 
> usual problem with circular type dependencies.  In this particular case, 
> it is because commands need to be represented as pipelines (instead of 
> string lists).  The pipelines are defined in Omake_shell_type, which 
> depends on Omake_env, but Omake_env needs the definition.
> 
> This issue comes up a lot.  The way we "solve" it now is one of two ways:
>    - make the types polymorphic over 'value, then instantiate them
>      in Omake_env
>    - move all their code into Omake_env
> This means Omake_env gets loaded with a lot of stuff.
> 
> The root of all this trouble is that the type venv is abstract, as it 
> should be.  But it means we can't just define all the types before 
> defining all the code, and so we get highly-constrained compile 
> dependencies.
> 
> I don't know of a good solution to this problem.  There are some 
> not-quite-satisfying ones:
>    1. Make the type venv public, and tell programmers not to use it
>       directly.
>    2. Keep it abstract, but define a bunch of constructors/destructors.
>       This is basically the same as making it public.
>    3. Define a "unpack_venv_hack : venv -> venv_internal = %identity"
>       so we can grep for occurrences.
>    4. Keep on using our current scheme, and allow Omake_env to
>       keep growing as we add unrelated stuff to it.
> 
> Perhaps there is another way?

Perhaps investigate the new mutually recursive modules support that was 
added to OCaml recently? Not sure if this can help us here.

In any case, it seems that if we decide to do any sort of polymorphic or 
functorized approach, the dependency should be not on 'value, but on 
'venv and 'env - after all these are the types that are "responsible" 
for the mess.

Also, from my (possibly overly conservative) POV it seems like any such 
significant refactoring belongs on 0.9.7 branch (after we merge the 
recent 0.9.6 changes).

-- 
Aleksey Nogin

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