Re: [Caml-list] standard regex package

[Gerd Stolpmann <info@gerd-stolpmann.de>]

On Thu, 23 Aug 2001, Benjamin C. Pierce wrote:
>> For those who don't know: You can
>> install almost every 3rd party Perl package by simply doing
>> 
>> perl Makefile.pl
>> make
>> make test
>> make install
>> 
>> It is simple to do, and that's an important aspect of the success of Perl (a
>> language which is nothing without CPAN).
>
>Having just spent 90 minutes last weekend trying to get a PERL package
>installed and working, I can say with confidence that PERL's standard
>installation procedure, while slick, leaves one big thing to be desired:
>following dependencies.  The problem with the "CPAN way" is that it leads
>to 10,000 people writing cool little packages, all of which depend on ten
>other cool little packages written by somebody else, etc., etc.
>Following all these dependency chains manually by trying to install one
>package, failing, grepping around in CPAN for the ones it depends on,
>downloading them, trying to install, failing, ... is a pretty boring way
>to spend a morning.
>
>I really wish that I'd been able to say to some tool, "I want to use
>module X; please go off to CPAN and find, download, and install me the
>current versions of X and all the modules it transitively depends on."  I
>know that it would be reallyreally hard to design a framework that would
>always do the right thing, but if it did the right thing 99% of the time
>and gave me a type error in 99% of the cases where it did not do the
>right thing, it would be fantastic (and I believe both of these numbers
>would be rather easy to achieve by low-tech means).

The CPAN module does it; see perldoc CPAN.

For O'Caml the corresponding functionality would be much harder because
of possible version conflicts. Say you have packages A and B already installed,
and A depends on B. Furthermore, you want to install package C, but package C
requires the new version B'. For Perl, this is less dramatic than it seems to
be because everything is dynamic, and the packages can themselves cope with
version conflicts. For Caml, a clever automatic installer must decide:

- Does the already installed package A work with the new version B'? If yes, 
  is it necessary to recompile package A?

- If package A must be renewed, too: Is there a version A' that works with B'?

- If there are other packages that depend on A: Is it necessary to
  recompile/relink them?

Because these questions are difficult, findlib does not include versioned
dependencies (but it includes versions as such, and dependencies as such). So
it requires still an intelligent operator that helps finding the right versions.

One feature that should be added is automatic recompilation of dependent
packages (from known sources).

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