website: Add post about Guix Packager.

* website/posts/guix-packager.md,
website/static/blog/img/guix-packager.gif: New files.

Co-authored-by: Philippe Virouleau <philippe.virouleau@inria.fr>

website/posts/guix-packager.md

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+title: Write package definitions in a breeze
+author: Ludovic Courtès, Philippe Virouleau
+tags: Scheme API, Programming interfaces
+date: 2023-11-24 14:30
+---
+
+More than 28,000 packages are available in Guix today, not counting
+third-party channels.  That’s a lot—the [5th largest GNU/Linux
+distro](https://repology.org/)!  But it’s nothing if the one package you
+care about is missing.  So even you, dear reader, may one day find
+yourself defining a package for your beloved deployment tool.  This post
+introduces a new tool poised to significantly lower the barrier to
+writing new packages.
+
+# Introducing Guix Packager
+
+[Defining
+packages](https://guix.gnu.org/manual/devel/en/html_node/Defining-Packages.html)
+for Guix is not all that hard but, as always, it’s much harder the first
+time you do it, especially when starting from a blank page and/or not
+being familiar with the programming environment of Guix.  [Guix
+Packager](https://guix-hpc.gitlabpages.inria.fr/guix-packager/) is a new
+web user interface to get you started—[try
+it!](https://guix-hpc.gitlabpages.inria.fr/guix-packager/).  It arrived
+right in time as an aid to the [packaging
+tutorial](https://hpc.guix.info/events/2023/workshop/program/#how-to-get-started-writing-guix-packages)
+given last week at the Workshop on Reproducible Software Environments.
+
+![Screenshot showing the Guix Packager interface.](/static/blog/img/guix-packager.gif)
+
+The interface aims to be intuitive: fill in forms on the left
+and it produces a correct, ready-to-use package definition on the right.
+Importantly, it helps you avoid pitfalls that trip up many newcomers:
+
+  - When you add a dependency in one of the “Inputs” fields, it adds the
+    right variable name in the generated code *and* imports the right
+    [package
+    module](https://guix.gnu.org/manual/devel/en/html_node/Package-Modules.html).
+  - Likewise, you can choose a license and be sure the `license` field
+    will refer to the right variable representing that license.
+  - You can turn tests on and off, and add configure flags.  These
+    translate to a valid `arguments` field of your package, letting you
+    discover the likes of [keyword
+    arguments](https://guix.gnu.org/cookbook/en/html_node/A-Scheme-Crash-Course.html)
+    and
+    [G-expressions](https://guix.gnu.org/manual/en/html_node/G_002dExpressions.html)
+    without having to first dive into the manual.
+
+Pretty cool, no?
+
+# Implementation
+
+All the credit for this tool goes to co-worker and intrepid hacker
+Philippe Virouleau.  A unique combination of paren aversion and web
+development superpowers—unique in the Guix community—led
+Philippe to develop the whole thing in a glimpse (says Ludovic!).
+
+The purpose was to provide a single view to be able to edit a package recipe,
+therefore the application is a *single-page application* (SPA) written in
+using the UI library Philippe is most comfortable with: [React](https://react.dev/),
+and [MaterialUI](https://mui.com/material-ui/) for styling the components.
+It's built with [TypeScript](https://www.typescriptlang.org/), and the library
+part actually defines all the types needed to manipulate Guix packages and their
+components (such as build systems or package sources).
+One of the more challenging parts was to be able to provide fast and helpful “search as you
+type” results over the 28k+ packages. It required a combination of
+MaterialUI's [virtualized inputs](https://mui.com/material-ui/react-autocomplete/#virtualization),
+as well as caching the packages data in the browser's local storage,
+when possible (packaging metadata itself is fetched from
+`https://guix.gnu.org/packages.json`, a generic representation of the
+current package set).
+
+While the feature set provides a great starting point, there are still a few
+things that may be worth implementing.  For instance, only the GNU and
+CMake build systems are supported so far; it would make sense to include
+a few others (Python-related ones might be good candidates).
+
+Running a local (development) version of the application can happen on
+top of Guix, since—obviously—it's been developed with the `node`
+version packaged in Guix, using the quite standard `packages.json` for
+JavaScript dependencies installed through `npm`.  [Contributions
+welcome!](https://gitlab.inria.fr/guix-hpc/guix-packager/)
+
+# Lowering the barrier to entry
+
+This neat tool complements a set of steps we’ve taken over time to make
+packaging in Guix approachable.  Indeed, while package definitions are
+actually code written in the Scheme language, the `package` “language”
+was designed [from the get-go](https://arxiv.org/abs/1305.4584) to be
+fully declarative—think JSON with parens instead of curly braces and
+semicolons.  More recently we [simplified the way package inputs are
+specified](https://guix.gnu.org/en/blog/2021/the-big-change/) with an
+eye on making package definitions less intimidating.
+
+The [`guix import`
+command](https://guix.gnu.org/manual/devel/en/html_node/Invoking-guix-import.html)
+also exists to make it easier to simplify packaging: it can generate a
+package definition for anything available in other package
+repositories such as PyPI, CRAN, Crates.io, and so forth.  If your
+preference goes to curly braces rather than parens, it can also [convert
+a JSON package
+description](https://guix.gnu.org/manual/devel/en/html_node/Invoking-guix-import.html#index-JSON_002c-import)
+to Scheme code.  Once you have your first `.scm` file, `guix build`
+prints hints for common errors such missing module imports (those
+`#:use-module` stanzas).  We also put effort into providing [reference
+documentation](https://guix.gnu.org/manual/devel/en/html_node/Defining-Packages.html),
+a [video
+tutorial](https://guix.gnu.org/en/videos/2020/packaging-part-two/), and
+a [tutorial for more complex
+packages](https://guix.gnu.org/cookbook/en/html_node/Packaging-Tutorial.html).
+
+Do share your experience [with us](https://guix.gnu.org/contact) and
+until then, happy packaging!
+
+# Acknowledgments
+
+Thanks to Felix Lechner and Timothy Sample for providing feedback on an
+earlier draft of this post.
+
+#### About GNU Guix
+
+[GNU Guix](https://guix.gnu.org) is a transactional package manager and
+an advanced distribution of the GNU system that [respects user
+freedom](https://www.gnu.org/distros/free-system-distribution-guidelines.html).
+Guix can be used on top of any system running the Hurd or the Linux
+kernel, or it can be used as a standalone operating system distribution
+for i686, x86_64, ARMv7, AArch64 and POWER9 machines.
+
+In addition to standard package management features, Guix supports
+transactional upgrades and roll-backs, unprivileged package management,
+per-user profiles, and garbage collection.  When used as a standalone
+GNU/Linux distribution, Guix offers a declarative, stateless approach to
+operating system configuration management.  Guix is highly customizable
+and hackable through [Guile](https://www.gnu.org/software/guile)
+programming interfaces and extensions to the
+[Scheme](http://schemers.org) language.