RE: [Caml-list] open Module (not?) considered harmful

["David Allsopp" <dra-news@metastack.com>]

On 20 November 2008 10:49, Stefano Zacchiroli wrote:
> On Thu, Nov 20, 2008 at 10:33:03AM +0000, Richard Jones wrote:
> > Encouraging developers to open modules is also usually a bad idea,
> > except in very limited circumstances (hello Printf).
> 
> Why? You and others failed me to convince of this. Or, better, I'm
> sure there are problems with that, but they just show deficiencies
> inherited from other parts of the language.
 
Consider

open Array;;
open List;;

(* Hundreds of lines of code *)

length [];;

The code is now is brittle in terms of the order of the open statements at
the top of the file and will fail to compile if they're swapped. Of course,
if you don't care about that kind of subtle refactoring error then open is
completely fine. Personally, I find that kind of brittleness irritating -
and it also has the potential to waste a huge amount of time if you have to
refactor the code.

Whether you find code less readable with or without module names is of
course a matter taste and IIRC, OCaml 3.11 .annot files contain the
necessary information to expand them so there could be a nice editor plugin
to expand or remove module paths...

> >   The most straightforward solution to this problem to me looks like
> >   providing a syntax equivalent like "from Module import foo, bar"
> >   which selectively imports only some identifiers from a given module.

Which, for values only, is of course a trivial camlp4 extension... and could
be generalised to include type declarations and so on with only a little
more work. The .NET languages have a syntax for selectively importing
classes from a namespace rather than the entire namespace (and it's
different from Java's in that you can rename the class while you do it).


David