Re: How to build a file which depends on the actual contents of store items?

[宋文武 <iyzsong@openmailbox.org>]

On 2015-11-20 22:12, ludo@gnu.org wrote:
> 宋文武 <iyzsong@openmailbox.org> skribis:
> 
> [...]
> 
>> +  (define (module-path module)
>> +    (list "  ModulePath \"" module "/lib/xorg/modules\"\n"))
> 
> [...]
> 
>> +" (apply string-append (map module-path modules)) "
> 
> As with NixOS, the solution is to move these computations to the “build
> side” (info "(guix) G-Expressions").
> 
> So you could do something like:
> 
>   (define build
>     #~(call-with-output-file #$output
>         (lambda (port)
>           (for-each emit-driver-stanza '#$@xorg-modules))))
> 
>   (gexp->derivation "xorg.conf" build)
> 
> Does that make sense?
Oh, yes!  I get what I want by replace mixed-text-file with 
gexp->derivation.

While the former is convient for concat strings and packages,
it doesn't have the '#:modules' argument, so I can't do:
   (mixed-text-file "xserver.conf"
     #~(begin (use-modules (guix build utils)) ... (find-files ...

> 
> The big difference with Nix is that we use the same language on both
> sides, so it’s easy to move things from one side to another, but it’s
> also easy to forget about the tradeoffs.
OK, I'm more comfortable with gexp now, thanks!