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  91 <header id="title-block-header">
  92 <h1 class="title">Advent of Code 2023</h1>
  93 </header>
  94 <p>Code to solve the <a href="http://adventofcode.com/2023/">Advent of
  95 Code</a> puzzles. This year, I’m using the puzzles to develop my skills
  96 in <a href="https://wiki.haskell.org/Haskell">Haskell</a>. I’m writing
  97 up a <a href="https://work.njae.me.uk/tag/advent-of-code/">commentary on
  98 these puzzles and my solutions</a> on my blog.</p>
  99 <p><a href="http://learnyouahaskell.com/chapters">Learn you a
 100 Haskell</a>, <a
 101 href="https://www.haskell.org/tutorial/index.html">Introduction to
 102 Haskell 98</a>, and <a href="https://hackage.haskell.org/">Hackage</a>
 103 are good resources.</p>
 104 <p>The <a href="https://cabal.readthedocs.io/en/latest/index.html">Cabal
 105 user guide</a> and <a href="http://howistart.org/posts/haskell/1/">How I
 106 Start: Haskell</a> are good sources of using the tools.</p>
 107 <h1 id="toolchain">Toolchain</h1>
 108 <p>Install Ghcup following <a
 109 href="https://www.haskell.org/ghcup/install/#installation">the
 110 instructions</a>, making sure to load the updated environment with</p>
 111 <div class="sourceCode" id="cb1"><pre
 112 class="sourceCode bash"><code class="sourceCode bash"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="bu">source</span> /home/neil/.ghcup/env</span></code></pre></div>
 113 <p>and then set the default GHC to use with
 114 <code>ghcup set ghc 9.0.1</code> .</p>
 115 <p>Install <a
 116 href="https://haskell-language-server.readthedocs.io/en/latest/configuration.html">Haskell
 117 Language Server</a> for Sublime Text</p>
 118 <h2 id="creating-the-repository-and-project">Creating the repository and
 119 project</h2>
 120 <p>Create the repository as normal: create the project in Gitolite,
 121 clone it, and insert the <code>.gitignore</code> and
 122 <code>README.md</code> files.</p>
 123 <p>There’s one package per day, with the code for each package in
 124 sub-directories of the root directory.</p>
 125 <p>Create the basic <code>cabal</code> project.</p>
 126 <pre><code>cabal init</code></pre>
 127 <p>Modify the <code>advent-of-code21.cabal</code> file as needed, such
 128 as updating the Cabal version and writing the <code>common</code>
 129 stanzas.</p>
 130 <h2 id="creating-subsequent-days">Creating subsequent days</h2>
 131 <p>Each day lives in a separate directory, with code in the
 132 <code>src</code> directory.</p>
 133 <p>Compile with</p>
 134 <pre><code>cabal build</code></pre>
 135 <p>or</p>
 136 <pre><code>cabal build advent01</code></pre>
 137 <p>Run with</p>
 138 <pre><code>cabal run advent01</code></pre>
 139 <p>If you want to pass in additional RTS parameters, do it like
 140 this:</p>
 141 <pre><code>cabal run advent01 -- +RTS -K0 -RTS</code></pre>
 142 <p>Run interactively with</p>
 143 <pre><code>cabal repl advent01</code></pre>
 144 <p>or</p>
 145 <pre><code>stack ghci advent01:exe:advent01</code></pre>
 146 <p>if the first form is ambiguous.</p>
 147 <h2 id="profiling">Profiling</h2>
 148 <p>To profile, use</p>
 149 <pre><code>cabal run advent01 --enable-profiling -- +RTS -N -p -s -hT</code></pre>
 150 <p>Or, you can simplify the RTS options by adding them to a new stanza
 151 in the cabal file:</p>
 152 <pre><code>executable advent01prof
 153   import: common-extensions, build-directives
 154   main-is: advent01/Main.hs
 155   build-depends: text, containers, linear, array, pqueue, mtl, lens
 156   ghc-options:         -O2
 157                        -Wall
 158                        -threaded
 159                        -eventlog
 160                        -rtsopts &quot;-with-rtsopts=-N -p -s -hT&quot;</code></pre>
 161 <p>Only include the <code>-eventlog</code> directive if you want to use
 162 Threadscope to investigate parallel behaviour.</p>
 163 <p>then running</p>
 164 <pre><code>cabal run advent01prof --enable-profiling</code></pre>
 165 <p>Generate the profile graph with</p>
 166 <pre><code>hp2ps -M advent01.hp</code></pre>
 167 <h1 id="packages">Packages</h1>
 168 <p>Packages I used a lot:</p>
 169 <ul>
 170 <li><a
 171 href="https://hackage.haskell.org/package/containers">Containers</a>
 172 (and some <a
 173 href="https://haskell-containers.readthedocs.io/en/latest/intro.html">better
 174 documentation</a>); <a
 175 href="https://hackage.haskell.org/package/unordered-containers">Unordered
 176 containers</a> is a mostly-equivalent alternative.</li>
 177 <li><a
 178 href="https://hackage.haskell.org/package/attoparsec">Attoparsec</a>
 179 (and <a
 180 href="https://hackage.haskell.org/package/megaparsec">Megaparsec</a>,
 181 and <a
 182 href="https://hackage.haskell.org/package/base-4.14.1.0/docs/Text-ParserCombinators-ReadP.html">ReadP</a>
 183 once).</li>
 184 </ul>
 185 <p>There are somewhat decent <a
 186 href="https://markkarpov.com/tutorial/megaparsec.html">tutorials on
 187 Megaparsec</a> and <a
 188 href="https://www.schoolofhaskell.com/school/starting-with-haskell/libraries-and-frameworks/text-manipulation/attoparsec">Attoparsec</a>.</p>
 189 <p>Packages I didn’t use much, but need to remember:</p>
 190 <ul>
 191 <li><a href="https://hackage.haskell.org/package/arithmoi">Arithmoi</a>
 192 for number theory</li>
 193 <li><a
 194 href="https://hackage.haskell.org/package/pointedlist-0.6.1">Pointed
 195 List</a> for zipper lists (sometimes circular)</li>
 196 <li><a href="https://hackage.haskell.org/package/vector">Vector</a> for
 197 array-like things</li>
 198 <li><a href="https://hackage.haskell.org/package/linear">Linear</a> for
 199 coordinate-vector like things</li>
 200 <li><a href="https://hackage.haskell.org/package/grid">Grid</a> for 2-d
 201 grids</li>
 202 <li><a
 203 href="https://hackage.haskell.org/package/graph-wrapper">Graph-wrapper</a>
 204 for graphs</li>
 205 <li><a href="https://hackage.haskell.org/package/lens">Lens</a> (and a
 206 <a href="https://github.com/ekmett/lens/wiki/Operators">summary of
 207 operators</a>). I didn’t use these much this year, but did a lot last
 208 year.</li>
 209 <li><a
 210 href="https://hackage.haskell.org/package/mtl-2.2.2/docs/Control-Monad-RWS-Lazy.html">RWS</a>
 211 (Reader-Writer-State monad stack); again, used a lot last year but not
 212 this year</li>
 213 <li><a
 214 href="https://hackage.haskell.org/package/monad-loops-0.4.3/docs/Control-Monad-Loops.html">Monad
 215 loops</a>, and <a
 216 href="https://conscientiousprogrammer.com/blog/2015/12/11/24-days-of-hackage-2015-day-11-monad-loops-avoiding-writing-recursive-functions-by-refactoring/">a
 217 description</a></li>
 218 <li><a
 219 href="https://github.com/jamesdbrock/replace-megaparsec">Replace-Megaparsec</a>,
 220 for using Mpc for all sorts of things traditionally done with regex
 221 substitutions.</li>
 222 </ul>
 223 <h1 id="readme">Readme</h1>
 224 <p>Build this readme file wth</p>
 225 <pre><code>pandoc -s README.md &gt; README.html</code></pre>
 226 <p>(Using the <a href="https://github.com/markdowncss/modest">Modest
 227 style</a>.)</p>
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