[bug#39945] [PATCH 0/1] Introducing 'with-parameters' for gexp dynamic binding

[Ludovic Courtès]

Hello Guix!

This patch adds a new ‘with-parameters’ form.  It is like ‘parameterize’
except that it takes effect when a file-like object is lowered, as in:

  ;; Return coreutils for i686.
  (with-parameters ((%current-system "i686-linux"))
    coreutils)

‘with-parameters’ is necessary because if you would use ‘parameterize’
in the example above, it wouldn’t have any effect at all: the dynamic
binding would be installed at the wrong time.

It works for any SRFI-39 parameter, though ‘%current-system’ is my main
use case.  It makes it possible to have gexps or manifests that include
things explicitly targeting a given system.  (For instance, I’d like to
have a manifest for release-critical things that explicitly pins the
targeted systems.)

Note that ‘with-parameters’ applies to file-like objects; it is _not_ a
property of the gexp itself.  So one cannot, for example, write:

  (with-parameters ((%current-system "i686-linux"))
    #~(a b c d))

I feel like it’s better this way, though it could be confusing.

Thoughts?

Besides, ‘with-parameters’ is the dual of what was discussed at
<https://issues.guix.gnu.org/issue/29296>.

Thanks,
Ludo’.

Ludovic Courtès (1):
  gexp: Add 'with-parameters'.

 .dir-locals.el |  1 +
 doc/guix.texi  | 19 ++++++++++++++++
 guix/gexp.scm  | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++
 tests/gexp.scm | 28 ++++++++++++++++++++++++
 4 files changed, 107 insertions(+)

-- 
2.25.1