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Re: nesting with-imported-modules

From: Ricardo Wurmus
Subject: Re: nesting with-imported-modules
Date: Thu, 20 Feb 2020 10:01:05 +0100
User-agent: mu4e 1.2.0; emacs 26.3

Ludovic Courtès <address@hidden> writes:

> Hello!
> Ricardo Wurmus <address@hidden> skribis:
>> it seems that it is impossible to nest with-imported-modules.  A gexp
>> that is wrapped in multiple layers of with-imported-modules won’t depend
>> on the list of all mentioned modules but only on the outermost.
>> This is because with-imported-modules sets the current-imported-modules
>> parameter without checking if the parameter already has a value.
>> Should nesting be supported?  It seems useful.
> Is it?  :-)
> My impression is that one would always write:
>   (with-imported-modules … #~(…))
> or possibly combining multiple expressions:
>   (define e1 (with-imported-modules … #~(…)))
>   (define e2 (with-imported-modules … #~(… #$e1 …)))
> in which case modules are appended.
> I couldn’t think of a use case where one would literally write:
>   (with-imported-modules …
>     (with-imported-modules …
>       #~(…)))

No, I’m not writing this literally, but I have an expression that uses
(guix search-paths), for example.  Then I have another procedure that
takes this expression and wraps it with an expression that uses (gnu
build linux-container).

--8<---------------cut here---------------start------------->8---
(define (containerize exp)
  (with-imported-modules (… (gnu build linux-container) …)
        (use-modules (gnu build linux-container))

(define (generate-exp)
  (define exp
    (with-imported-modules (… (guix search-paths) …)
          (use-modules (guix search-paths))
   (if container? (containerize exp) exp))
--8<---------------cut here---------------end--------------->8---

The observed effect was that only one of the with-imported-modules calls
had any effect on the final expression.


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