A technically unnecessary but hopefully interesting introduction: One cool thing about Gnu Guix is the ability to use manifests, which are a declarative definition of the package outputs of a profile. In other words, instead of running the commands
guix install emacs
guix install frozen-bubble
guix install gitYou can just have a manifest file like
(specifications->manifest
'("emacs"
"frozen-bubble"
"git"))saved in a file, say, “christopher-home.scm”, and then feed it into the package manager to define your whole package profile at once:
guix package -m /home/christopher/Manifests/christopher-home.scmThat is nice, because then you can just edit that file to change your package set. Also, you can backup that file, copy it to another computer, or put it under version control.
Another great feature of Guix is the ability to have multiple profiles. A profile is basically a set of package outputs that are exposed in the same place with accompanying environment information. My default profile is programs, libraries, etc. that I want to have easy access to most of the time (not including their dependencies, which is another matter taken care of “behind the scene”). But I can create another profile that just exposes a few programs and libraries that I need for some special purpose.
Probably the most likely example would be certain libraries or programs needed for building or for running some piece of downloaded software. My real life example is trying to run the downloaded (pre-built) version of the Arduino IDE, which is not yet packaged in Guix. To do this I needed some particular system libraries, as well as Java, leading to this specification:
(use-modules (gnu packages gcc))
(concatenate-manifests
(list
(specifications->manifest
'("avr-toolchain"
"dfu-programmer"
"gcc-toolchain"
"glibc"
"icedtea"
"libx11"
"libxrandr"
"libxtst"))
(packages->manifest
`((,gcc "lib")))))In my case, I install this profile with
guix package -m /home/christopher/Manifests/arduino.scm -p /home/christopher/.guix-extra-profiles/arduino/arduinoAnd so we come to the ostensible purpose of this post, to describe two features useful in constructing manifests, not really covered well in the Guix reference manual:
First, there is the concatenate-manifests procedure from the (guix profiles) module. This allows you to combine together a manifest constructed by specifications->manifest, along with one constructed by packages->manifest. For most packages you want to use specifications->manifest, because that convenient procedure saves you the bother of having to explicitly import the required package definitions. But, sometimes you need packages->manifest, which leads to the second thing I wanted to mention:
When using packages->manifest, you can specify your manifest entries as tuples containing the package object followed by a string describing the specific package output you need. In my case, this is critical, as I need to use the “hidden” package gcc (in order, if you must know, to get the libstdc++ library exposed) as well as the specific package output lib, since the default output did not expose the required library.
Further reading:
The Libre Hacker 