Re: Order of *CENTRAL-REGISTRY* traversal

I think that whether or not this is done there should be some  
standardized interface to the *central-registry* and to the whole  
system lookup process. Part of this would be something like:

add-path-to-registry <path> &optional (precedence :higher)
remove-path <path>
map-paths <fn>

There could also be a mechanism that would realize that a system can  
be found in multiple places and provides a call back to break ties  
(perhaps defaulting to the most recent / highest version).

Either of these proposals is likely to get overly complex fast (which  
perhaps means that they aren't a good idea! <sad face>) but I think  
that exposing the *central-registry* variable is a bad idea...


On Dec 7, 2005, at 3:00 AM, Nikodemus Siivola wrote:

> (This is parallel to my earlier note about SB-EXT:*MODULE-PROVIDER- 
> FUNCTIONS* traversal.)
>
> Currently ASDF traverses *CENTRAL-REGISTRY* head-to-tail: new  
> locations pushed to the front take precendence and older ones serve  
> as fallbacks. The behaviour undocumented.
>
> I believe that this is an unfortunate design as it means that a  
> seemingly
> innocent PUSH can lead to totally different set of libraries being  
> loaded
> as would be without. The system is unstable: a single idiomatic  
> operation
> can have large and impossible to predict consequences.
>
> I would like to change ASDF to traverse it tail to head instead, so  
> that (PUSH <DIR> *CENTRAL-REGISTRY*) can only make a previously  
> failing (OOS 'LOAD-OP :FOO) succeed, but not alter the behaviour of  
> a succeeding operation.
>
> This _would_ cause migration work for people whose setups  
> deliberately operate on the head or tail already. However, I doubt  
> this is much depended on outside personal initialization files  
> since the current behaviour is not only undocumented but unstable.
>
> Cheers,
>
>  -- Nikodemus              Schemer: "Buddha is small, clean, and  
> serious."
>                   Lispnik: "Buddha is big, has hairy armpits, and  
> laughs."
>
>
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