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Re: REPL example session for overriding a package?

From: Ludovic Courtès
Subject: Re: REPL example session for overriding a package?
Date: Tue, 24 Jan 2017 15:56:17 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)

Hi Myles,

Myles English <address@hidden> skribis:

> I am trying to make a package that inherits from an existing package and
> overrides a *minimum* number of elements of the original package
> definition.
> Probably the most efficient way to do this would be to try out some
> things in the REPL using tools from (gnu packages).  Having read a bit
> about it I am finding it difficult to get my head around working in the
> REPL, does anyone have an example session?
> - get an element of a package definition
> - substitute a nested element
> Specifically, for the package eigen in (gnu packages algebra) I'd like
> to remove, or maybe add to, the snippet.

Maybe something like this:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use(gnu packages algebra)
scheme@(guile-user)> ,use(guix)
scheme@(guile-user)> (define my-eigen
                         (inherit eigen)
                         (source (origin
                                   (inherit (package-source eigen))
                                       ,(origin-snippet (package-source eigen))
                                       (display "hey there!\n")))))))
scheme@(guile-user)> (origin-snippet (package-source my-eigen))
$3 = (begin (substitute* "CMakeLists.txt" …))
--8<---------------cut here---------------end--------------->8---

The snippet here is really pasting together two pieces of code
(imperative code), which can be brittle (“unhygienic” in macro



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