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doc: Finish importing the "Packaging Tutorial". 

* doc/guix-cookbook.texi (Packaging Tutorial): Import all sections after the
  Scheme crash course.
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@ -331,6 +331,7 @@ It does not assume much knowledge of the Guix system nor of the Lisp language.
The reader is only expected to be familiar with the command line and to have some
basic programming knowledge.
@node A "Hello World" package
@subsection A "Hello World" package
The “Defining Packages” section of the manual introduces the basics of Guix
@ -521,8 +522,785 @@ We've gone as far as we could without any knowledge of Scheme. Before moving
on to more complex packages, now is the right time to brush up on your Scheme
knowledge. @pxref{A Scheme Crash Course} to get up to speed.
@c TODO: Continue the tutorial
@node Setup
@subsection Setup
In the rest of this chapter we will rely on some basic Scheme
programming knowledge. Now let's detail the different possible setups
for working on Guix packages.
There are several ways to set up a Guix packaging environment.
We recommend you work directly on the Guix source checkout since it makes it
easier for everyone to contribute to the project.
But first, let's look at other possibilities.
@node Local file
@subsubsection Local file
This is what we previously did with @samp{my-hello}. With the Scheme basics we've
covered, we are now able to explain the leading chunks. As stated in @code{guix
package --help}:
@example
-f, --install-from-file=FILE
install the package that the code within FILE
evaluates to
@end example
Thus the last expression @emph{must} return a package, which is the case in our
earlier example.
The @code{use-modules} expression tells which of the modules we need in the file.
Modules are a collection of values and procedures. They are commonly called
"libraries" or "packages" in other programming languages.
@node @samp{GUIX_PACKAGE_PATH}
@subsubsection @samp{GUIX_PACKAGE_PATH}
@emph{Note: Starting from Guix 0.16, the more flexible Guix "channels" are the
preferred way and supersede @samp{GUIX_PACKAGE_PATH}. See next section.}
It can be tedious to specify the file from the command line instead of simply
calling @code{guix package --install my-hello} as you would do with the official
packages.
Guix makes it possible to streamline the process by adding as many "package
declaration paths" as you want.
Create a directory, say @samp{~./guix-packages} and add it to the @samp{GUIX_PACKAGE_PATH}
environment variable:
@example
$ mkdir ~/guix-packages
$ export GUIX_PACKAGE_PATH=~/guix-packages
@end example
To add several directories, separate them with a colon (@code{:}).
Our previous @samp{my-hello} needs some adjustments though:
@example
(define-module (my-hello)
#:use-module (guix licenses)
#:use-module (guix packages)
#:use-module (guix build-system gnu)
#:use-module (guix download))
(define-public my-hello
(package
(name "my-hello")
(version "2.10")
(source (origin
(method url-fetch)
(uri (string-append "mirror://gnu/hello/hello-" version
".tar.gz"))
(sha256
(base32
"0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
(build-system gnu-build-system)
(synopsis "Hello, Guix world: An example custom Guix package")
(description
"GNU Hello prints the message \"Hello, world!\" and then exits. It
serves as an example of standard GNU coding practices. As such, it supports
command-line arguments, multiple languages, and so on.")
(home-page "https://www.gnu.org/software/hello/")
(license gpl3+)))
@end example
Note that we have assigned the package value to an exported variable name with
@code{define-public}. This is effectively assigning the package to the @code{my-hello}
variable so that it can be referenced, among other as dependency of other
packages.
If you use @code{guix package --install-from-file=my-hello.scm} on the above file, it
will fail because the last expression, @code{define-public}, does not return a
package. If you want to use @code{define-public} in this use-case nonetheless, make
sure the file ends with an evaluation of @code{my-hello}:
@example
; ...
(define-public my-hello
; ...
)
my-hello
@end example
This last example is not very typical.
Now @samp{my-hello} should be part of the package collection like all other official
packages. You can verify this with:
@example
$ guix package --show=my-hello
@end example
@node Guix channels
@subsubsection Guix channels
Guix 0.16 features channels, which is very similar to @samp{GUIX_PACKAGE_PATH} but
provides better integration and provenance tracking. Channels are not
necessarily local, they can be maintained as a public Git repository for
instance. Of course, several channels can be used at the same time.
@xref{Channels,,, guix, GNU Guix Reference Manual} for setup details.
@node Direct checkout hacking
@subsubsection Direct checkout hacking
Working directly on the Guix project is recommended: it reduces the friction
when the time comes to submit your changes upstream to let the community benefit
from your hard work!
Unlike most software distributions, the Guix repository holds in one place both
the tooling (including the package manager) and the package definitions. This
choice was made so that it would give developers the flexibility to modify the
API without breakage by updating all packages at the same time. This reduces
development inertia.
Check out the official @uref{https://git-scm.com/, Git} repository:
@example
$ git clone https://git.savannah.gnu.org/git/guix.git
@end example
In the rest of this article, we use @samp{$GUIX_CHECKOUT} to refer to the location of
the checkout.
Follow the instruction in the manual (@pxref{Contributing,,, guix, GNU Guix
Reference Manual}) to set up the repository environment.
Once ready, you should be able to use the package definitions from the
repository environment.
Feel free to edit package definitions found in @samp{$GUIX_CHECKOUT/gnu/packages}.
The @samp{$GUIX_CHECKOUT/pre-inst-env} script lets you use @samp{guix} over the package
collection of the repository.
@itemize
@item
Search packages, such as Ruby:
@example
$ cd $GUIX_CHECKOUT
$ ./pre-inst-env guix package --list-available=ruby
ruby 1.8.7-p374 out gnu/packages/ruby.scm:119:2
ruby 2.1.6 out gnu/packages/ruby.scm:91:2
ruby 2.2.2 out gnu/packages/ruby.scm:39:2
@end example
@item
Build a package, here Ruby version 2.1:
@example
$ ./pre-inst-env guix build --keep-failed ruby@@2.1
/gnu/store/c13v73jxmj2nir2xjqaz5259zywsa9zi-ruby-2.1.6
@end example
@item
Install it to your user profile:
@example
$ ./pre-inst-env guix package --install ruby@@2.1
@end example
@item
Check for common mistakes:
@example
$ ./pre-inst-env guix lint ruby@@2.1
@end example
@end itemize
Guix strives at maintaining a high packaging standard; when contributing to the
Guix project, remember to
@itemize
@item
follow the coding style (@pxref{Coding Style,,, guix, GNU Guix Reference Manual}),
@item
and review the check list from the manual (@pxref{Submitting Patches,,, guix, GNU Guix Reference Manual}).
@end itemize
Once you are happy with the result, you are welcome to send your contribution to
make it part of Guix. This process is also detailed in the manual. (@pxref{Contributing,,, guix, GNU Guix Reference Manual})
It's a community effort so the more join in, the better Guix becomes!
@node Extended example
@subsection Extended example
The above "Hello World" example is as simple as it goes. Packages can be more
complex than that and Guix can handle more advanced scenarios. Let's look at
another, more sophisticated package (slightly modified from the source):
@example
(define-module (gnu packages version-control)
#:use-module ((guix licenses) #:prefix license:)
#:use-module (guix utils)
#:use-module (guix packages)
#:use-module (guix git-download)
#:use-module (guix build-system cmake)
#:use-module (gnu packages ssh)
#:use-module (gnu packages web)
#:use-module (gnu packages pkg-config)
#:use-module (gnu packages python)
#:use-module (gnu packages compression)
#:use-module (gnu packages tls))
(define-public my-libgit2
(let ((commit "e98d0a37c93574d2c6107bf7f31140b548c6a7bf")
(revision "1"))
(package
(name "my-libgit2")
(version (git-version "0.26.6" revision commit))
(source (origin
(method git-fetch)
(uri (git-reference
(url "https://github.com/libgit2/libgit2/")
(commit commit)))
(file-name (git-file-name name version))
(sha256
(base32
"17pjvprmdrx4h6bb1hhc98w9qi6ki7yl57f090n9kbhswxqfs7s3"))
(patches (search-patches "libgit2-mtime-0.patch"))
(modules '((guix build utils)))
(snippet '(begin
;; Remove bundled software.
(delete-file-recursively "deps")
#t))))
(build-system cmake-build-system)
(outputs '("out" "debug"))
(arguments
`(#:tests? #t ; Run the test suite (this is the default)
#:configure-flags '("-DUSE_SHA1DC=ON") ; SHA-1 collision detection
#:phases
(modify-phases %standard-phases
(add-after 'unpack 'fix-hardcoded-paths
(lambda _
(substitute* "tests/repo/init.c"
(("#!/bin/sh") (string-append "#!" (which "sh"))))
(substitute* "tests/clar/fs.h"
(("/bin/cp") (which "cp"))
(("/bin/rm") (which "rm")))
#t))
;; Run checks more verbosely.
(replace 'check
(lambda _ (invoke "./libgit2_clar" "-v" "-Q")))
(add-after 'unpack 'make-files-writable-for-tests
(lambda _ (for-each make-file-writable (find-files "." ".*")))))))
(inputs
`(("libssh2" ,libssh2)
("http-parser" ,http-parser)
("python" ,python-wrapper)))
(native-inputs
`(("pkg-config" ,pkg-config)))
(propagated-inputs
;; These two libraries are in 'Requires.private' in libgit2.pc.
`(("openssl" ,openssl)
("zlib" ,zlib)))
(home-page "https://libgit2.github.com/")
(synopsis "Library providing Git core methods")
(description
"Libgit2 is a portable, pure C implementation of the Git core methods
provided as a re-entrant linkable library with a solid API, allowing you to
write native speed custom Git applications in any language with bindings.")
;; GPLv2 with linking exception
(license license:gpl2))))
@end example
(In those cases were you only want to tweak a few fields from a package
definition, you should rely on inheritance instead of copy-pasting everything.
See below.)
Let's discuss those fields in depth.
@subsubsection @code{git-fetch} method
Unlike the @code{url-fetch} method, @code{git-fetch} expects a @code{git-reference} which takes
a Git repository and a commit. The commit can be any Git reference such as
tags, so if the @code{version} is tagged, then it can be used directly. Sometimes
the tag is prefixed with a @code{v}, in which case you'd use @code{(commit (string-append
"v" version))}.
To ensure that the source code from the Git repository is stored in a unique
directory with a readable name we use @code{(file-name (git-file-name name
version))}.
Note that there is also a @code{git-version} procedure that can be used to derive the
version when packaging programs for a specific commit.
@subsubsection Snippets
Snippets are quoted (i.e. non-evaluated) Scheme code that are a means of patching
the source. They are a Guix-y alternative to the traditional @samp{.patch} files.
Because of the quote, the code in only evaluated when passed to the Guix daemon
for building.
There can be as many snippet as needed.
Snippets might need additional Guile modules which can be imported from the
@code{modules} field.
@subsubsection Inputs
First, a syntactic comment: See the quasi-quote / comma syntax?
@example
(native-inputs
`(("pkg-config" ,pkg-config)))
@end example
is equivalent to
@example
(native-inputs
(list (list "pkg-config" pkg-config)))
@end example
You'll mostly see the former because it's shorter.
There are 3 different input types. In short:
@table @asis
@item native-inputs
Required for building but not runtime -- installing a package
through a substitute won't install these inputs.
@item inputs
Installed in the store but not in the profile, as well as being
present at build time.
@item propagated-inputs
Installed in the store and in the profile, as well as
being present at build time.
@end table
@xref{Package Reference,,, guix, GNU Guix Reference Manual} for more details.
The distinction between the various inputs is important: if a dependency can be
handled as an @emph{input} instead of a @emph{propagated input}, it should be done so, or
else it "pollutes" the user profile for no good reason.
For instance, a user installing a graphical program that depends on a
command line tool might only be interested in the graphical part, so there is no
need to force the command line tool into the user profile. The dependency is a
concern to the package, not to the user. @emph{Inputs} make it possible to handle
dependencies without bugging the user by adding undesired executable files (or
libraries) to their profile.
Same goes for @emph{native-inputs}: once the program is installed, build-time
dependencies can be safely garbage-collected.
It also matters when a substitute is available, in which case only the @emph{inputs}
and @emph{propagated inputs} will be fetched: the @emph{native inputs} are not required to
install a package from a substitute.
@subsubsection Outputs
Just like how a package can have multiple inputs, it can also produce multiple
outputs.
Each output corresponds to a separate directory in the store.
The user can choose which output to install; this is useful to save space or
to avoid polluting the user profile with unwanted executables or libraries.
Output separation is optional. When the @code{outputs} field is left out, the
default and only output (the complete package) is referred to as @code{"out"}.
Typical separate output names include @code{debug} and @code{doc}.
It's advised to separate outputs only when you've shown it's worth it: if the
output size is significant (compare with @code{guix size}) or in case the package is
modular.
@subsubsection Build system arguments
The @code{arguments} is a keyword-value list used to configure the build process.
The simplest argument @code{#:tests?} can be used to disable the test suite when
building the package. This is mostly useful when the package does not feature
any test suite. It's strongly recommended to keep the test suite on if there is
one.
Another common argument is @code{:make-flags}, which specifies a list of flags to
append when running make, as you would from the command line. For instance, the
following flags
@example
#:make-flags (list (string-append "prefix=" (assoc-ref %outputs "out"))
"CC=gcc")
@end example
translate into
@example
$ make CC=gcc prefix=/gnu/store/...-<out>
@end example
This sets the C compiler to @code{gcc} and the @code{prefix} variable (the installation
directory in Make parlance) to @code{(assoc-ref %outputs "out")}, which is a build-stage
global variable pointing to the destination directory in the store (something like
@samp{/gnu/store/...-my-libgit2-20180408}).
Similarly, it's possible to set the "configure" flags.
@example
#:configure-flags '("-DUSE_SHA1DC=ON")
@end example
The @code{%build-inputs} variable is also generated in scope. It's an association
table that maps the input names to their store directories.
The @code{phases} keyword lists the sequential steps of the build system. Typically
phases include @code{unpack}, @code{configure}, @code{build}, @code{install} and @code{check}. To know
more about those phases, you need to work out the appropriate build system
definition in @samp{$GUIX_CHECKOUT/guix/build/gnu-build-system.scm}:
@example
(define %standard-phases
;; Standard build phases, as a list of symbol/procedure pairs.
(let-syntax ((phases (syntax-rules ()
((_ p ...) `((p . ,p) ...)))))
(phases set-SOURCE-DATE-EPOCH set-paths install-locale unpack
bootstrap
patch-usr-bin-file
patch-source-shebangs configure patch-generated-file-shebangs
build check install
patch-shebangs strip
validate-runpath
validate-documentation-location
delete-info-dir-file
patch-dot-desktop-files
install-license-files
reset-gzip-timestamps
compress-documentation)))
@end example
Or from the REPL:
@example
> (add-to-load-path "/path/to/guix/checkout")
> ,module (guix build gnu-build-system)
> (map first %standard-phases)
(set-SOURCE-DATE-EPOCH set-paths install-locale unpack bootstrap patch-usr-bin-file patch-source-shebangs configure patch-generated-file-shebangs build check install patch-shebangs strip validate-runpath validate-documentation-location delete-info-dir-file patch-dot-desktop-files install-license-files reset-gzip-timestamps compress-documentation)
@end example
If you want to know more about what happens during those phases, consult the
associated procedures.
For instance, as of this writing the definition of @code{unpack} for the GNU build
system is
@example
(define* (unpack #:key source #:allow-other-keys)
"Unpack SOURCE in the working directory, and change directory within the
source. When SOURCE is a directory, copy it in a sub-directory of the current
working directory."
(if (file-is-directory? source)
(begin
(mkdir "source")
(chdir "source")
;; Preserve timestamps (set to the Epoch) on the copied tree so that
;; things work deterministically.
(copy-recursively source "."
#:keep-mtime? #t))
(begin
(if (string-suffix? ".zip" source)
(invoke "unzip" source)
(invoke "tar" "xvf" source))
(chdir (first-subdirectory "."))))
#t)
@end example
Note the @code{chdir} call: it changes the working directory to where the source was
unpacked.
Thus every phase following the @code{unpack} will use the source as a working
directory, which is why we can directly work on the source files.
That is to say, unless a later phase changes the working directory to something
else.
We modify the list of @code{%standard-phases} of the build system with the
@code{modify-phases} macro as per the list of specified modifications, which may have
the following forms:
@itemize
@item
@code{(add-before PHASE NEW-PHASE PROCEDURE)}: Run @code{PROCEDURE} named @code{NEW-PHASE} before @code{PHASE}.
@item
@code{(add-after PHASE NEW-PHASE PROCEDURE)}: Same, but afterwards.
@item
@code{(replace PHASE PROCEDURE)}.
@item
@code{(delete PHASE)}.
@end itemize
The @code{PROCEDURE} supports the keyword arguments @code{inputs} and @code{outputs}. Each
input (whether @emph{native}, @emph{propagated} or not) and output directory is referenced
by their name in those variables. Thus @code{(assoc-ref outputs "out")} is the store
directory of the main output of the package. A phase procedure may look like
this:
@example
(lambda* (#:key inputs outputs #:allow-other-keys)
(let (((bash-directory (assoc-ref inputs "bash"))
(output-directory (assoc-ref outputs "out"))
(doc-directory (assoc-ref outputs "doc"))
; ...
#t)
@end example
The procedure must return @code{#t} on success. It's brittle to rely on the return
value of the last expression used to tweak the phase because there is no
guarantee it would be a @code{#t}. Hence the trailing @code{#t} to ensure the right value
is returned on success.
@subsubsection Code staging
The astute reader may have noticed the quasi-quote and comma syntax in the
argument field. Indeed, the build code in the package declaration should not be
evaluated on the client side, but only when passed to the Guix daemon. This
mechanism of passing code around two running processes is called @uref{https://arxiv.org/abs/1709.00833, code staging}.
@subsubsection "Utils" functions
When customizing @code{phases}, we often need to write code that mimics the
equivalent system invocations (@code{make}, @code{mkdir}, @code{cp}, etc.) commonly used during
regular "Unix-style" installations.
Some like @code{chmod} are native to Guile.
@xref{,,, guile, Guile reference manual} for a complete list.
Guix provides additional helper functions which prove especially handy in the
context of package management.
Some of those functions can be found in
@samp{$GUIX_CHECKOUT/guix/guix/build/utils.scm}. Most of them mirror the behaviour
of the traditional Unix system commands:
@table @asis
@item which
Like the @samp{which} system command.
@item find-files
Akin to the @samp{find} system command.
@item mkdir-p
Like @samp{mkdir -p}, which creates all parents as needed.
@item install-file
Similar to @samp{install} when installing a file to a (possibly
non-existing) directory. Guile has @code{copy-file} which works
like @samp{cp}.
@item copy-recursively
Like @samp{cp -r}.
@item delete-file-recursively
Like @samp{rm -rf}.
@item invoke
Run an executable. This should be used instead of @code{system*}.
@item with-directory-excursion
Run the body in a different working directory,
then restore the previous working directory.
@item substitute*
A "sed-like" function.
@end table
@subsubsection Module prefix
The license in our last example needs a prefix: this is because of how the
@code{license} module was imported in the package, as @code{#:use-module ((guix licenses)
#:prefix license:)}. The Guile module import mechanism
(@pxref{Using Guile Modules,,, guile, Guile reference manual})
gives the user full control over namespacing: this is needed to avoid
clashes between, say, the
@samp{zlib} variable from @samp{licenses.scm} (a @emph{license} value) and the @samp{zlib} variable
from @samp{compression.scm} (a @emph{package} value).
@node Other build systems
@subsection Other build systems
What we've seen so far covers the majority of packages using a build system
other than the @code{trivial-build-system}. The latter does not automate anything
and leaves you to build everything manually. This can be more demanding and we
won't cover it here for now, but thankfully it is rarely necessary to fall back
on this system.
For the other build systems, such as ASDF, Emacs, Perl, Ruby and many more, the
process is very similar to the GNU build system except for a few specialized
arguments.
Learn more about build systems in
@itemize
@item
@uref{https://www.gnu.org/software/guix/manual/en/html_node/Build-Systems.html#Build-Systems, the manual, section 4.2 Build systems},
@item
the source code in the @samp{$GUIX_CHECKOUT/guix/build} and
@samp{$GUIX_CHECKOUT/guix/build-system} directories.
@end itemize
@node Programmable and automated package definition
@subsection Programmable and automated package definition
We can't repeat it enough: having a full-fledged programming language at hand
empowers us in ways that reach far beyond traditional package management.
Let's illustrate this with some awesome features of Guix!
@node Recursive importers
@subsubsection Recursive importers
You might find some build systems good enough that there is little to do at all
to write a package, to the point that it becomes repetitive and tedious after a
while. A @emph{raison d'être} of computers is to replace human beings at those
boring tasks. So let's tell Guix to do this for us and create the package
definition of an R package from CRAN (the output is trimmed for conciseness):
@example
$ guix import cran --recursive walrus
(define-public r-mc2d
; ...
(license gpl2+)))
(define-public r-jmvcore
; ...
(license gpl2+)))
(define-public r-wrs2
; ...
(license gpl3)))
(define-public r-walrus
(package
(name "r-walrus")
(version "1.0.3")
(source
(origin
(method url-fetch)
(uri (cran-uri "walrus" version))
(sha256
(base32
"1nk2glcvy4hyksl5ipq2mz8jy4fss90hx6cq98m3w96kzjni6jjj"))))
(build-system r-build-system)
(propagated-inputs
`(("r-ggplot2" ,r-ggplot2)
("r-jmvcore" ,r-jmvcore)
("r-r6" ,r-r6)
("r-wrs2" ,r-wrs2)))
(home-page "https://github.com/jamovi/walrus")
(synopsis "Robust Statistical Methods")
(description
"This package provides a toolbox of common robust statistical
tests, including robust descriptives, robust t-tests, and robust ANOVA.
It is also available as a module for 'jamovi' (see
<https://www.jamovi.org> for more information). Walrus is based on the
WRS2 package by Patrick Mair, which is in turn based on the scripts and
work of Rand Wilcox. These analyses are described in depth in the book
'Introduction to Robust Estimation & Hypothesis Testing'.")
(license gpl3)))
@end example
The recursive importer won't import packages for which Guix already has package
definitions, except for the very first.
Not all applications can be packaged this way, only those relying on a select
number of supported systems. Read about the full list of importers in
the guix import section of the manual
(@pxref{Invoking guix import,,, guix, GNU Guix Reference Manual}).
@node Automatic update
@subsubsection Automatic update
Guix can be smart enough to check for updates on systems it knows. It can
report outdated package definitions with
@example
$ guix refresh hello
@end example
In most cases, updating a package to a newer version requires little more than
changing the version number and the checksum. Guix can do that automatically as
well:
@example
$ guix refresh hello --update
@end example
@node Inheritance
@subsubsection Inheritance
If you've started browsing the existing package definitions, you might have
noticed that a significant number of them have a @code{inherit} field:
@example
(define-public adwaita-icon-theme
(package (inherit gnome-icon-theme)
(name "adwaita-icon-theme")
(version "3.26.1")
(source (origin
(method url-fetch)
(uri (string-append "mirror://gnome/sources/" name "/"
(version-major+minor version) "/"
name "-" version ".tar.xz"))
(sha256
(base32
"17fpahgh5dyckgz7rwqvzgnhx53cx9kr2xw0szprc6bnqy977fi8"))))
(native-inputs
`(("gtk-encode-symbolic-svg" ,gtk+ "bin")))))
@end example
All unspecified fields are inherited from the parent package. This is very
convenient to create alternative packages, for instance with different source,
version or compilation options.
@node Getting help
@subsection Getting help
Sadly, some applications can be tough to package. Sometimes they need a patch to
work with the non-standard filesystem hierarchy enforced by the store.
Sometimes the tests won't run properly. (They can be skipped but this is not
recommended.) Other times the resulting package won't be reproducible.
Should you be stuck, unable to figure out how to fix any sort of packaging
issue, don't hesitate to ask the community for help.
See the @uref{https://www.gnu.org/software/guix/contact/, Guix homepage} for information on the mailing lists, IRC, etc.
@node Conclusion
@subsection Conclusion
This tutorial was a showcase of the sophisticated package management that Guix
boasts. At this point we have mostly restricted this introduction to the
@code{gnu-build-system} which is a core abstraction layer on which more advanced
abstractions are based.
Where do we go from here? Next we ought to dissect the innards of the build
system by removing all abstractions, using the @code{trivial-build-system}: this
should give us a thorough understanding of the process before investigating some
more advanced packaging techniques and edge cases.
Other features worth exploring are the interactive editing and debugging
capabilities of Guix provided by the Guile REPL@.
Those fancy features are completely optional and can wait; now is a good time
to take a well-deserved break. With what we've introduced here you should be
well armed to package lots of programs. You can get started right away and
hopefully we will see your contributions soon!
@node References
@subsection References
@itemize
@item
The @uref{https://www.gnu.org/software/guix/manual/en/html_node/Defining-Packages.html, package reference in the manual}
@item
@uref{https://gitlab.com/pjotrp/guix-notes/blob/master/HACKING.org, Pjotr’s hacking guide to GNU Guix}
@item
@uref{https://www.gnu.org/software/guix/guix-ghm-andreas-20130823.pdf, "GNU Guix: Package without a scheme!"}, by Andreas Enge
@end itemize
@c *********************************************************************
@node System Configuration