Hi Ludo !

> Maybe with a macro along these lines:

Nice, thanks !

I attached the patch I come up with. It's working ok :)
I have a shorter version using match :

--8<---------------cut here---------------start------------->8---
(letrec-syntax ((maybe-load-paths
                 (syntax-rules ()
                   ((_ item rest ...)
                    (let ((tail (maybe-load-paths rest ...)))
                      (if (string? item)
                          (match tail
                            ((load-path load-compiled-path)
                            (list
                             (cons (string-append item
                                                  "/share/guile/site/"
                                                  #$(effective-version))
                                   load-path)
                             (cons (string-append item
                                                  "/lib/guile/"
                                                  #$(effective-version)
                                                  "/site-ccache")
                                   load-compiled-path))))
                          tail)))
                   ((_)
                    '(() ())))))
  (match (maybe-load-paths #$guile-json #$guile-ssh
                           #$guile-git #$guile-bytestructures)
    ((module-load-path module-load-compiled-path)
     (set! %load-path (append module-load-path %load-path)
     (set! %load-compiled-path (append module-load-compiled-path %load-compiled-path))))))
--8<---------------cut here---------------end--------------->8---

It might seems preferable but I can't get guix-latest derivation to
include (ice-9 match), maybe because of #:module-path in
"(gexp->derivation "guix-latest" ...".

Mathieu