> Yes, use the wonderful ‘define-record-type*’ from (guix utils).  This is
> what we use for ‘package’, etc.  See
> <http://lists.gnu.org/archive/html/guile-user/2012-11/msg00016.html>,
> for details.

I attached the draft.  (I remember about other issues.)

But it doesn't work.  These lines rise an error:

+                 (cons (gnu-package-descriptor
+                        (inherit (first state))
+                        ((eval (match-field str)
+                               (interaction-environment)) str))

(There may be other problems.  For instance, it should remove fields'
names from 'str' before creating a record.)

What do you think about the 'eval' idea?  It's used to avoid unnecessary
repetition.

I'll try to pinpoint the cause later.  Though, it will save a lot of
time if you tell that the whole idea is bad.  Or if you already know the
cause of the problem.

Also, is it possible to create a default value for a field (like #f)?