Re: [cclan-list] How do I replace my broken ':perform' forms?

[Thom G. <tho...@ma...>]

On Dec 8, 2008, at 11:47 AM, Robert Goldman wrote:

> Thom Goodsell wrote:
>> Sorry if this has been covered, or if it's just really obvious, but I
>> couldn't find anything helpful in the archives.
>>
>> I recently (i.e., about 15 minutes ago) got a new version of  
>> asdf.lisp
>> when I updated my copy of ccl, and it broke a behavior I've been
>> using. I *believe* that I was using the behavior incorrectly, and  
>> that
>> the change was a bugfix, though I could be misunderstanding the svn
>> logs.
>>
>> In my defsystem, I have the following bit of code:
>>
>>   :perform (load-op :before (op c)
>> 		    ;; the before method runs after dependencies are loaded,
>> 		    ;; but before the components are loaded, so clsql-mysql is
>> available
>> 		    (pushnew #p"/usr/local/mysql/lib/"      ; local development
>> 			     (symbol-value (find-symbol "*FOREIGN-LIBRARY-SEARCH-PATHS*"
>> 							:clsql-sys)))
>> 		    (asdf:oos 'asdf:load-op 'clsql-mysql))
>>
>> It appears, now, that my comment is not correct. The idea is that I
>> want to load all the systems from :depends-on, which includes clsql.
>> Then I want to set up clsql-sys:*foreign-library-search-paths* to
>> include the correct version of the MySQL libraries. Finally, I want  
>> to
>> load the mysql components of clsql.
>>
>> Does anyone have advice on the Right Way (or even just a good way) to
>> do this?
>>
>
> If I understand correctly, this won't work because the system itself
> undergoes the perform operation only /after/ all of its components
> undergo that operation.  I.e., if you have a system S with  
> components A
> and B, you'll see something like
>
> (perform <op> A) (perform <op> B) (perform <op> C)
>
> This has been a perpetual source of friction in using ASDF to do
> non-standard things.  For example, this is why I can't write  
> an :around
> method to dynamically bind a variable over the entire set of  
> operations
> on a system.
>
> What would be nice would be if the ASDF plan were to include a
> hierarchical structure something like:
>
> (perform <composite-op> S
>   :children
>   ((perform <op> A)
>   (perform <op> B)
>   (perform <op> C)))
>
> It's not obvious how to do this, though, since I think one could end  
> up
> with complex plans where the loading operations for a single component
> (S) are non-contiguous.
>
> There are various unpleasant kludges around this.  For your case, I
> would suggest making a faux system something like
>
> (defsystem clsql-version-identifier
>   :depends-on (:clsql)
>   :perform ... generalization of your :before method here...
> )
>
> Then make your *real* system depend on clsql-version-identifier.
>
> Note that I have NOT tried this, and I have a vague memory that ASDF  
> may
> behave oddly when given a system that has no components.  You'll  
> have to
> investigate this yourself.
>
> Alternatively, can't you just define a method like
>
> (defmethod perform :after ((op load-op) (c (find-system 'clsql- 
> mysql)))
>   ....)

For the record, this was the approach I ended up using (though the  
proper specialization is "(eql (find-system 'clsql-mysql))". After  
considering the other recommendations, this seemed like the best  
option for me. I do not intend to distribute this system (it's the key  
piece of our corporate IP), and my personal preference is to keep  
system startup as simple as possible, which I felt means keeping this  
functionality within the asd file so my start script can just load the  
system and start.

Thanks, all, for the suggestions.

Thom