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

[Robert G. <rpg...@si...>]

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)))
   ....)

This may be tricky, though, to get the find-system to work properly when
this perform method definition is read...

Best,
r