Re: New module system option :duplicates

[Marius Vollmer <mvo@zagadka.de>]

Mikael Djurfeldt <djurfeldt@nada.kth.se> writes:

> Marius Vollmer <mvo@zagadka.de> writes:
> 
> > Just giving the license to merge any and all generics that have
> > colliding names is probably not what one wants.
> 
> Actually, I'd like to have the option to do exactly that.  In my view,
> we can reasonably safely regard the merging as an administrative
> non-issue for most programs.

I see, yes.  Unasked merging of generics has usually very few if any
negative consequences.

But still, you can not really savely use a generic that has been
merged from two generics without your explicit consent.

The typical situation would be that one part of a module intents to
use the one generic, while another part (written later or by a
different person) intents to use a second generic that happens to have
the same name.  The second part will likely add another ":use-module"
clause and ":duplicates merge-generics" will silently merge the two
generics.

When the two generics have non-overlapping type signatures for their
signatures, all is well.  But you can't be sure about this.  You need
to be made aware that there is a collision/merging going on and then
you can declare that this specific merge is OK.  

I guess it is next to impossible to automatically check whether
overlapping type signatures can be merged the Right Way.
  
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