From e66bf31656e853da331fb0124ebff19e5ac03c0d Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Thu, 20 Jun 2019 11:48:21 +0200
Subject: WIPc

---
 index.html | 256 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 240 insertions(+), 16 deletions(-)

diff --git a/index.html b/index.html
index 9cb33a6..102acdf 100644
--- a/index.html
+++ b/index.html
@@ -31,7 +31,7 @@
          background: none !important;
          border: none !important;
          box-shadow: none !important;
-         font-size: 0.45em !important;
+         font-size: 0.4em !important;
      }
 
      .caption {
@@ -71,15 +71,16 @@
           <h1>Perl software in<br>GNU Guix</h1>
 
           <aside class="notes" data-markdown>
-            Hello, my name is Chris, and I'm talking about package
-            management with GNU Guix.
+            Hello, my name is Chris, and I'm talking about GNU Guix
+            and Perl, mostly Guix.
 
-            I first found out about Guix sometime in late 2015, early
-            2016.
+            You might know Perl, it's a very established programming
+            language.
 
-            I remember installing it the night before FOSDEM back in
-            2016 and I started using and contributing to Guix soon
-            after.
+            GNU Guix is a more recent project, it started in
+            2012. It's a package manager, and distribution of the GNU
+            system.
+          </aside>
         </section>
 
         <section>
@@ -89,6 +90,20 @@
           <p>Get and use Perl modules</p>
 
           <p>Get and use tools and applications written in Perl</p>
+
+          <aside class="notes" data-markdown>
+            Perl is an important component for Guix as a package
+            manager, as many other packages depend on Perl at build
+            time, or runtime.
+
+            It's also something Guix can help you use. If you want to
+            run Perl, you can use Guix to install it.
+
+            Guix also packages some Perl (around 700) modules.
+
+            There's also software packaged for Guix that's written in
+            Perl, and I'll mention a couple of examples.
+          </aside>
         </section>
 
         <section>
@@ -96,12 +111,20 @@
 
           <pre>→ guix install perl
 
+...
+
 → perl --version
 
 This is perl 5, version 28, subversion 0 (v5.28.0) built for
 x86_64-linux-thread-multi
 
 ...</pre>
+
+          <aside class="notes" data-markdown>
+            Back to getting Perl though. Installing packages through
+            Guix is quite simple, you can run the `guix install`
+            command with the name of the package.
+          </aside>
         </section>
 
         <section>
@@ -110,11 +133,31 @@ x86_64-linux-thread-multi
           <pre>
 → guix install perl perl-uri
 
+...
+
 → echo $PERL5LIB
 /gnu/store/h3ryiwyhp8qcxyf74sxyv746171zpazr-profile/lib/perl5/site_perl
 
 → ls /gnu/store/h3r...azr-profile/lib/perl5/site_perl/5.28.0/
 URI  URI.pm  x86_64-linux-thread-multi</pre>
+
+          <aside class="notes" data-markdown>
+            Installing Perl with some modules is very similar.
+
+            Note here that these modules have to be specifically
+            packaged for Guix, more about that later.
+
+            If you're familiar with other distributions that use a
+            more standard filesystem hierarchy, Guix isn't like that.
+
+            Most things end up in the `/gnu/store` directory. Guix
+            however, does understand that Perl uses the PERL5LIB
+            environment variable to find things within the `lib/perl5/site_perl`
+            directory within packages, so when it creates a profile, a
+            grouping together of packages, it'll group the Perl
+            modules together, and include the appropriate value for
+            the `PERL5LIB` environment variable.
+          </aside>
         </section>
 
         <section data-background="white">
@@ -125,6 +168,18 @@ URI  URI.pm  x86_64-linux-thread-multi</pre>
             <li>Static site generator</li>
             <li>I occasionally use it for blogging</li>
           </ul>
+
+          <aside class="notes" data-markdown>
+            On to some software that's written in Perl.
+
+            Ikiwiki is a wiki compiler, built around a flexible static
+            site generator. I personally use it for simple websites
+            and blogs.
+
+            It's written in Perl, and I was using it before I started
+            using Guix. It was also absent from Guix back then, so I
+            packaged it, and some of it's missing dependencies.
+          </aside>
         </section>
 
         <section>
@@ -146,6 +201,14 @@ in repository guix.
        new  f0539b6   gnu: Add perl-cgi-session.
        new  909dcf5   gnu: Add ikiwiki.
           </pre>
+
+          <aside class="notes" data-markdown>
+            I don't want to spend too much time on this, but I thought
+            it might be useful to skim over the Guix package
+            definition for Ikiwiki. It's too long to fit on one slide,
+            but hopefully this'll give you an idea of what goes in to
+            a Guix package.
+          </aside>
         </section>
 
         <section>
@@ -163,12 +226,37 @@ in repository guix.
        (sha256
         (base32
          <span class="string">"17pyblaqhkb61lxl63bzndiffism8k859p54k3k4sghclq6lsynh"</span>))))</span>
-<span class="fragment fade-in">...</span>
-</pre></section>
+  <span class="fragment fade-in">...</span></pre>
+
+          <aside class="notes" data-markdown>
+            Packages in Guix are defined through a record type in
+            Guile scheme. I've only done a little bit of Perl
+            programming, but I think it has a concept of a record as
+            well.
+
+            So, `define-public ikiwiki` is defining a value called
+            `ikiwiki`, which is a package.
+
+            (next)
+
+            Next there are some fields in the package record. The
+            package has a name, and the version is also specified.
+
+            (next)
+
+            Then the `source` is defined. This says to fetch something
+            from a URL. In this case, the Ikiwiki package is a little
+            odd. Normally this would be a release tarball from the
+            upstream authors, not the snapshot.debian.org site.
+
+            Importantly, the expected hash of the file is also
+            specified. This means there'll be no surprises, and that
+            the behaviour will be consistent in to the future. 
+          </aside>
+        </section>
 
         <section>
-          <pre>
-<span style="opacity: 0.5;">(<span class="yellow-keyboard">define-public</span> ikiwiki
+          <pre><span style="opacity: 0.5;">(<span class="yellow-keyboard">define-public</span> ikiwiki
   (package</span>
     ...
     <span class="fragment fade-in-then-semi-out">(build-system perl-build-system)</span>
@@ -199,7 +287,40 @@ in repository guix.
                              `(<span class="string">"PERL5LIB"</span> <span class="string">":"</span> prefix (,path))))
                          (find-files bin))
              #t))))))</span>
-<span class="fragment fade-in">...</span></pre></section>
+  <span class="fragment fade-in">...</span></pre>
+
+          <aside class="notes" data-markdown>
+            Moving on, each package has a build system. There are
+            quite a few build systems, each representing common build
+            steps that apply to multiple packages.
+
+            In this case, Ikiwiki uses the perl-build-system. This
+            will look for files like Build.PL and Makefile.PL, and use
+            them if they exist.
+
+            (next)
+
+            The build system can be passed some arguments. Here, some
+            of the phases of the build process are being tweaked.
+
+            (next)
+
+            After the `'unpack` phase, there's a small change being
+            made to the source code. The value of the PERL5LIB
+            environment variable is being included in a file. This is
+            so Ikiwiki can find the modules it requires at runtime.
+
+            (next)
+
+            The Makefile is then patched to have the example
+            configuration installed. Often this isn't necessary.
+
+            Finally, one common step is wrapping the files within the
+            bin directory with the value of the PERL5LIB environment
+            variable. This is also to ensure that Ikiwiki can find the
+            modules it requires at runtime.
+          </aside>
+        </section>
 
         <section>
 <pre><span style="opacity: 0.5;">(<span class="yellow-keyboard">define-public</span> ikiwiki
@@ -231,7 +352,46 @@ in repository guix.
        (<span class="string">"perl-text-markdown-discount"</span> ,perl-text-markdown-discount)
        (<span class="string">"perl-uri"</span> ,perl-uri)
        (<span class="string">"perl-yaml-libyaml"</span> ,perl-yaml-libyaml)))</span>
-<span class="fragment fade-in">...</span></pre></section>
+  <span class="fragment fade-in">...</span></pre>
+
+          <aside class="notes" data-markdown>
+            Next come the inputs to the package.
+
+            The terminology comes from the "functional" package
+            management paradigm that Guix uses. If you consider a
+            building a package a function, the dependencies are inputs
+            to that function, and the output of the function is the
+            built package in the store.
+
+            There are multiple types of inputs, native-inputs are
+            those that are just used at build time. Whereas inputs are
+            used at runtime, and maybe also when the package is being
+            built.
+
+            The distinction is mostly important when cross compiling,
+            something which the Perl build system doesn't currently
+            support as far as I'm aware.
+
+            Thinking back to the use of the PERL5LIB environment
+            variable on the previous slide, these are the modules
+            which will be mentioned in the value of that environment
+            variable.
+
+            When building a Guix package, the build process takes
+            place in an isolated environment, with only the store
+            items that the package and build system explicitly
+            require, along with their dependnecies.
+
+            Guix will ensure that any store item referenced by the
+            generated outputs exists within the store. Which it's why
+            it's important for the Ikiwiki package to reference the
+            modules it requires explicitly.
+
+            This is similar to what other package managers do with the
+            notion of dependencies, except in Guix it's much more
+            specific and unchanging.
+          </aside>
+        </section>
 
         <section>
 <pre><span style="opacity: 0.5;">(<span class="yellow-keyboard">define-public</span> ikiwiki
@@ -243,8 +403,13 @@ in repository guix.
      <span class="string">"Ikiwiki is a wiki compiler, capable of generating a static set of web
 pages, but also incorporating dynamic features like a web based editor and
 commenting."</span>)
-    (license license:gpl2+)))</span>
-          </pre>
+    (license license:gpl2+)))</span></pre>
+
+<aside class="notes" data-markdown>
+  Moving on, the last few fields within the package record are some
+  metadata, the home page, and license for the package, along with a
+  short synopsis and longer description.
+</aside>
         </section>
 
         <section>
@@ -255,6 +420,20 @@ commenting."</span>)
 
 <span class="fragment fade-right">/gnu/store/hcrv2cqzbisdb35hg2xmbxp1r2z7ijzd-ikiwiki-3.20190228</span>
           </pre>
+
+          <aside class="notes" data-markdown>
+            With this definition, we can instruct Guix to build the
+            Ikiwiki package.
+
+            Stuff may happen, then you should see the store item that
+            has been created.
+
+            The hash here in the name represents the process that's
+            gone in to creating this package. Including all the
+            inputs, the build system and the arguments in the package
+            definition. Change any of that, the hash will change, and
+            you'll get a different store item.
+          </aside>
         </section>
 
         <section>
@@ -291,10 +470,28 @@ commenting."</span>)
         └── man8
             └── ikiwiki-mass-rebuild.8.gz
           </pre>
+
+          <aside class="notes" data-markdown>
+            While Guix doesn't follow the same filesystem hierachy as
+            other distributions of GNU, what you find within the store
+            item for a package might be more familiar. Particularly
+            the bin, lib and share directories.
+
+            (Any questions about Ikiwiki?)
+          </aside>
         </section>
 
         <section data-background="white">
           <img src="sqitch-logo.svg" alt="Sqitch" style="width: 15em;" />
+
+          <ul>
+            <li>Sensible database change management</li>
+          </ul>
+
+          <aside class="notes" data-markdown>
+            Next, I thought I'd mention Sqitch. It's a database change
+            management tool that I've recently started using.
+          </aside>
         </section>
 
         <section>
@@ -320,6 +517,13 @@ in repository guix.
        new  55916fa   gnu: Add perl-mysql-config.
        new  7b23313   gnu: Add perl-string-shellquote.
        new  cabe8f1   gnu: Add sqitch.</pre>
+
+          <aside class="notes" data-markdown>
+            It's written in Perl, and I recently packaged it for
+            Guix. The process and package definition is similar to
+            Ikiwiki, this time, let's look at packaging one of the
+            missing modules required by Sqitch.
+          </aside>
         </section>
 
         <section>
@@ -352,6 +556,20 @@ From http://www.cpan.org/authors/id/M/MI/MIYAGAWA/HTTP-Tinyish-0.15.tar.gz...
     <span class="string">"HTTP::Tiny compatible HTTP client wrappers"</span>)
   (description fill-in-yourself!)
   (license perl-license))</pre>
+
+          <aside class="notes" data-markdown>
+            Guix has several importers. These importers utilise the
+            information that already exists about packages to help
+            creating Guix package definitions.
+
+            In this case, the information from CPAN is used to fill in
+            some of the parts of the perl-http-tinyish package
+            definition.
+
+            Importers can make it much easier to create package
+            definitions for Perl modules, as well as lots of other
+            languages.
+          </aside>
         </section>
 
         <section>
@@ -361,6 +579,12 @@ From http://www.cpan.org/authors/id/M/MI/MIYAGAWA/HTTP-Tinyish-0.15.tar.gz...
           <p>Get and use Perl modules</p>
 
           <p>Get and use tools and applications written in Perl</p>
+
+          <aside class="notes" data-markdown>
+            So to recap, I haven't gone much in to the more general
+            what and why around Guix, but hopefully some of these Perl
+            examples have been useful.
+          </aside>
         </section>
       </div>
     </div>
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