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Amy de Buitléir 2025-08-19 21:29:26 +01:00
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@ -4,7 +4,7 @@
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="generator" content="Asciidoctor 2.0.20">
<meta name="generator" content="Asciidoctor 2.0.23">
<meta name="author" content="Amy de Buitléir">
<title>Wombat&#8217;s Book of Nix</title>
<style>
@ -33,6 +33,7 @@ pre.pygments .tok-c1 { color: #3D7B7B; font-style: italic } /* Comment.Single */
pre.pygments .tok-cs { color: #3D7B7B; font-style: italic } /* Comment.Special */
pre.pygments .tok-gd { color: #A00000 } /* Generic.Deleted */
pre.pygments .tok-ge { font-style: italic } /* Generic.Emph */
pre.pygments .tok-ges { font-weight: bold; font-style: italic } /* Generic.EmphStrong */
pre.pygments .tok-gr { color: #E40000 } /* Generic.Error */
pre.pygments .tok-gh { color: #000080; font-weight: bold } /* Generic.Heading */
pre.pygments .tok-gi { color: #008400 } /* Generic.Inserted */
@ -474,7 +475,7 @@ The sound of water
<div class="sect3">
<h4 id="type-path">2.2.5. Paths</h4>
<div class="paragraph">
<p>File paths are play an important role in building software, so Nix has a special data type for them.
<p>File paths play an important role in building software, so Nix has a special data type for them.
Paths may be absolute (e.g. <code>/bin/sh</code>) or relative (e.g. <code>./data/file1.csv</code>).
Note that paths are not enclosed in quotation marks; they are not strings!</p>
</div>
@ -634,7 +635,7 @@ Within the REPL, type <code>:?</code> to see a list of available commands.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="pygments highlight nowrap"><code><span></span>$# echo &quot;$ nix repl&quot;
<pre class="pygments highlight nowrap"><code><span></span>$ nix repl
Welcome to Nix 2.18.1. Type :? for help.
nix-repl&gt; :?
@ -2008,42 +2009,42 @@ is always called <code>flake.nix</code>.</p>
<span class="tok-c1"># See https://github.com/mhwombat/nix-for-numbskulls/blob/main/flakes.md</span>
<span class="tok-c1"># for a brief overview of what each section in a flake should or can contain.</span>
<span class="tok-ss">description =</span> <span class="tok-s2">&quot;a very simple and friendly flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">description</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;a very simple and friendly flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">inputs =</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">inputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">outputs =</span> <span class="tok-p">{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-utils <span class="tok-p">}:</span>
<span class="tok-ss">outputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-utils <span class="tok-p">}:</span>
flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>eachDefaultSystem <span class="tok-p">(</span>system<span class="tok-p">:</span>
<span class="tok-k">let</span>
<span class="tok-ss">pkgs =</span> <span class="tok-nb">import</span> nixpkgs <span class="tok-p">{</span> <span class="tok-k">inherit</span> system<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">pkgs</span> <span class="tok-o">=</span> <span class="tok-nb">import</span> nixpkgs <span class="tok-p">{</span> <span class="tok-k">inherit</span> system<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-k">in</span>
<span class="tok-p">{</span>
<span class="tok-ss">packages =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello =</span> pkgs<span class="tok-o">.</span>stdenv<span class="tok-o">.</span>mkDerivation <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">name =</span> <span class="tok-s2">&quot;hello-flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">packages</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello</span> <span class="tok-o">=</span> pkgs<span class="tok-o">.</span>stdenv<span class="tok-o">.</span>mkDerivation <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">name</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;hello-flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">src =</span> <span class="tok-o">.</span><span class="tok-l">/.</span><span class="tok-p">;</span>
<span class="tok-ss">src</span> <span class="tok-o">=</span> <span class="tok-l">./.</span><span class="tok-p">;</span>
<span class="tok-ss">unpackPhase =</span> <span class="tok-s2">&quot;true&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">unpackPhase</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;true&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">buildPhase =</span> <span class="tok-s2">&quot;:&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">buildPhase</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;:&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">installPhase =</span>
<span class="tok-s1">&#39;&#39;</span>
<span class="tok-s1"> mkdir -p $out/bin</span>
<span class="tok-s1"> cp $src/hello-flake $out/bin/hello-flake</span>
<span class="tok-s1"> chmod +x $out/bin/hello-flake</span>
<span class="tok-s1"> &#39;&#39;</span><span class="tok-p">;</span>
<span class="tok-ss">installPhase</span> <span class="tok-o">=</span>
<span class="tok-s tok-s-Multiline">&#39;&#39;</span>
<span class="tok-s tok-s-Multiline"> mkdir -p $out/bin</span>
<span class="tok-s tok-s-Multiline"> cp $src/hello-flake $out/bin/hello-flake</span>
<span class="tok-s tok-s-Multiline"> chmod +x $out/bin/hello-flake</span>
<span class="tok-s tok-s-Multiline"> &#39;&#39;</span><span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">default =</span> hello<span class="tok-p">;</span>
<span class="tok-ss">default</span> <span class="tok-o">=</span> hello<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">apps =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello =</span> flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>mkApp <span class="tok-p">{</span> <span class="tok-ss">drv =</span> self<span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-err">$</span><span class="tok-p">{</span>system<span class="tok-p">}</span><span class="tok-o">.</span>hello<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">default =</span> hello<span class="tok-p">;</span>
<span class="tok-ss">apps</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello</span> <span class="tok-o">=</span> flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>mkApp <span class="tok-p">{</span> <span class="tok-ss">drv</span> <span class="tok-o">=</span> self<span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-si">${</span>system<span class="tok-si">}</span><span class="tok-o">.</span>hello<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">default</span> <span class="tok-o">=</span> hello<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-p">}</span>
<span class="tok-p">);</span>
@ -2060,9 +2061,9 @@ For now, I&#8217;d like to focus on the inputs section.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span><span class="tok-ss">inputs =</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span><span class="tok-ss">inputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<span class="tok-p">};</span></code></pre>
</div>
</div>
@ -2203,7 +2204,7 @@ without the version number</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>nixpkgs<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs/nixos&quot;</span><span class="tok-p">;</span></code></pre>
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>nixpkgs<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs/nixos&quot;</span><span class="tok-p">;</span></code></pre>
</div>
</div>
<div class="paragraph">
@ -2211,7 +2212,7 @@ without the version number</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>nixpkgs<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;nixpkgs&quot;</span><span class="tok-p">;</span></code></pre>
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>nixpkgs<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;nixpkgs&quot;</span><span class="tok-p">;</span></code></pre>
</div>
</div>
<div class="paragraph">
@ -2263,10 +2264,10 @@ flake references that you might encounter. This example</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>inputs<span class="tok-o">.</span><span class="tok-nb">import</span><span class="tok-ss">-cargo =</span> <span class="tok-p">{</span>
<span class="tok-ss">type =</span> <span class="tok-s2">&quot;github&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">owner =</span> <span class="tok-s2">&quot;edolstra&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">repo =</span> <span class="tok-s2">&quot;import-cargo&quot;</span><span class="tok-p">;</span>
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>inputs<span class="tok-o">.</span><span class="tok-nb">import</span><span class="tok-o">-</span><span class="tok-ss">cargo</span> <span class="tok-o">=</span> <span class="tok-p">{</span>
<span class="tok-ss">type</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">owner</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;edolstra&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">repo</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;import-cargo&quot;</span><span class="tok-p">;</span>
<span class="tok-p">};</span></code></pre>
</div>
</div>
@ -2275,7 +2276,7 @@ flake references that you might encounter. This example</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>inputs<span class="tok-o">.</span><span class="tok-nb">import</span><span class="tok-err">-</span>cargo<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:edolstra/import-cargo&quot;</span><span class="tok-p">;</span></code></pre>
<pre class="pygments highlight nowrap"><code data-lang="nix"><span></span>inputs<span class="tok-o">.</span><span class="tok-nb">import</span><span class="tok-o">-</span>cargo<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:edolstra/import-cargo&quot;</span><span class="tok-p">;</span></code></pre>
</div>
</div>
</td>
@ -2620,7 +2621,7 @@ will be added.</p>
<p><code>$system</code> is the system that the package is being built for.</p>
</li>
<li>
<p><code>$PWD</code> and <code>$TMP</code> both point to a temporary build directories</p>
<p><code>$PWD</code> and <code>$TMP</code> both point to temporary build directories</p>
</li>
<li>
<p><code>$HOME</code> and <code>$PATH</code> point to nonexistent directories, so the build
@ -2786,48 +2787,48 @@ The highlighted modifications below will accomplish that.</p>
<span class="tok-c1"># See https://github.com/mhwombat/nix-for-numbskulls/blob/main/flakes.md</span>
<span class="tok-c1"># for a brief overview of what each section in a flake should or can contain.</span>
<span class="tok-ss">description =</span> <span class="tok-s2">&quot;a very simple and friendly flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">description</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;a very simple and friendly flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">inputs =</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">inputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">outputs =</span> <span class="tok-p">{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-utils <span class="tok-p">}:</span>
<span class="tok-ss">outputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-utils <span class="tok-p">}:</span>
flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>eachDefaultSystem <span class="tok-p">(</span>system<span class="tok-p">:</span>
<span class="tok-k">let</span>
<span class="tok-ss">pkgs =</span> <span class="tok-nb">import</span> nixpkgs <span class="tok-p">{</span> <span class="tok-k">inherit</span> system<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">pkgs</span> <span class="tok-o">=</span> <span class="tok-nb">import</span> nixpkgs <span class="tok-p">{</span> <span class="tok-k">inherit</span> system<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-k">in</span>
<span class="tok-p">{</span>
<span class="hll"> <span class="tok-ss">devShells =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
</span><span class="hll"> <span class="tok-ss">default =</span> pkgs<span class="tok-o">.</span>mkShell <span class="tok-p">{</span>
</span><span class="hll"> <span class="tok-ss">packages =</span> <span class="tok-p">[</span> pkgs<span class="tok-o">.</span>cowsay <span class="tok-p">];</span>
<span class="hll"> <span class="tok-ss">devShells</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
</span><span class="hll"> <span class="tok-ss">default</span> <span class="tok-o">=</span> pkgs<span class="tok-o">.</span>mkShell <span class="tok-p">{</span>
</span><span class="hll"> <span class="tok-ss">packages</span> <span class="tok-o">=</span> <span class="tok-p">[</span> pkgs<span class="tok-o">.</span>cowsay <span class="tok-p">];</span>
</span><span class="hll"> <span class="tok-p">};</span>
</span><span class="hll"> <span class="tok-p">};</span>
</span>
<span class="tok-ss">packages =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello =</span> pkgs<span class="tok-o">.</span>stdenv<span class="tok-o">.</span>mkDerivation <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">name =</span> <span class="tok-s2">&quot;hello-flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">packages</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello</span> <span class="tok-o">=</span> pkgs<span class="tok-o">.</span>stdenv<span class="tok-o">.</span>mkDerivation <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">name</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;hello-flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">src =</span> <span class="tok-o">.</span><span class="tok-l">/.</span><span class="tok-p">;</span>
<span class="tok-ss">src</span> <span class="tok-o">=</span> <span class="tok-l">./.</span><span class="tok-p">;</span>
<span class="tok-ss">unpackPhase =</span> <span class="tok-s2">&quot;true&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">unpackPhase</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;true&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">buildPhase =</span> <span class="tok-s2">&quot;:&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">buildPhase</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;:&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">installPhase =</span>
<span class="tok-s1">&#39;&#39;</span>
<span class="tok-s1"> mkdir -p $out/bin</span>
<span class="tok-s1"> cp $src/hello-flake $out/bin/hello-flake</span>
<span class="tok-s1"> chmod +x $out/bin/hello-flake</span>
<span class="tok-s1"> &#39;&#39;</span><span class="tok-p">;</span>
<span class="tok-ss">installPhase</span> <span class="tok-o">=</span>
<span class="tok-s tok-s-Multiline">&#39;&#39;</span>
<span class="tok-s tok-s-Multiline"> mkdir -p $out/bin</span>
<span class="tok-s tok-s-Multiline"> cp $src/hello-flake $out/bin/hello-flake</span>
<span class="tok-s tok-s-Multiline"> chmod +x $out/bin/hello-flake</span>
<span class="tok-s tok-s-Multiline"> &#39;&#39;</span><span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">default =</span> hello<span class="tok-p">;</span>
<span class="tok-ss">default</span> <span class="tok-o">=</span> hello<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">apps =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello =</span> flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>mkApp <span class="tok-p">{</span> <span class="tok-ss">drv =</span> self<span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-err">$</span><span class="tok-p">{</span>system<span class="tok-p">}</span><span class="tok-o">.</span>hello<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">default =</span> hello<span class="tok-p">;</span>
<span class="tok-ss">apps</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello</span> <span class="tok-o">=</span> flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>mkApp <span class="tok-p">{</span> <span class="tok-ss">drv</span> <span class="tok-o">=</span> self<span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-si">${</span>system<span class="tok-si">}</span><span class="tok-o">.</span>hello<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">default</span> <span class="tok-o">=</span> hello<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-p">}</span>
<span class="tok-p">);</span>
@ -2908,7 +2909,7 @@ don&#8217;t need to <code>git push</code> the changes until we&#8217;re ready to
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ git commit hello-flake flake.nix -m 'added bovine feature'
[main c264cad] added bovine feature
[main 11a8ffe] added bovine feature
2 files changed, 7 insertions(+), 1 deletion(-)
$ nix run
________________________
@ -3082,7 +3083,7 @@ hyphenated and non-hyphenated versions of many Nix commands, and yes,
it&#8217;s confusing. The non-hyphenated commands were introduced when support
for flakes was added to Nix. I predict that eventually all hyphenated
commands will be replaced with non-hyphenated versions. Until then, a
useful rule of thumb is that non-hyphenated commands are for for working
useful rule of thumb is that non-hyphenated commands are for working
directly with flakes; hyphenated commands are for everything else.</p>
</div>
</td>
@ -3117,9 +3118,9 @@ You can come back to this section later to learn more.</p>
<pre class="nowrap">$ nix-shell -p ghc
$ runghc Main.hs
Main.hs:1:1: error:
Could not find module ‘Network.HostName’
Use -v (or `:set -v` in ghci) to see a list of the files searched for.
Main.hs:1:1: error: [GHC-87110]
Could not find module ‘Network.HostName’.
Use :set -v to see a list of the files searched for.
|
1 | import Network.HostName
| ^^^^^^^^^^^^^^^^^^^^^^^</pre>
@ -3136,9 +3137,9 @@ Let&#8217;s exit that shell and try again, this time adding the <code>hostname</
$ nix-shell -p "[ghc hostname]"
$ runghc Main.hs
Main.hs:1:1: error:
Could not find module ‘Network.HostName’
Use -v (or `:set -v` in ghci) to see a list of the files searched for.
Main.hs:1:1: error: [GHC-87110]
Could not find module ‘Network.HostName’.
Use :set -v to see a list of the files searched for.
|
1 | import Network.HostName
| ^^^^^^^^^^^^^^^^^^^^^^^</pre>
@ -3159,9 +3160,9 @@ The package we want is in the <em>package set</em> called <code>haskellPackages<
$ nix-shell -p "[ghc haskellPackages.hostname]"
$ runghc Main.hs
Main.hs:1:1: error:
Could not find module ‘Network.HostName’
Use -v (or `:set -v` in ghci) to see a list of the files searched for.
Main.hs:1:1: error: [GHC-87110]
Could not find module ‘Network.HostName’.
Use :set -v to see a list of the files searched for.
|
1 | import Network.HostName
| ^^^^^^^^^^^^^^^^^^^^^^^</pre>
@ -3214,6 +3215,11 @@ Your hostname is: wombat11k</pre>
<div class="paragraph">
<p>Success! Now we know the program works.</p>
</div>
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ exit</pre>
</div>
</div>
</div>
</div>
<div class="sect3">
@ -3250,10 +3256,11 @@ This is just an ordinary Cabal file; we don&#8217;t need to do anything special
<span class="normal">23</span>
<span class="normal">24</span>
<span class="normal">25</span>
<span class="normal">26</span></pre></div></td><td class="code"><div><pre><span></span>cabal-version: 3.0
<span class="normal">26</span>
<span class="normal">27</span></pre></div></td><td class="code"><div><pre><span></span>cabal-version: 3.0
name: hello-flake-haskell
version: 1.0.0
synopsis: A simple demonstration using a Nix flake to package a Haskell program that prints a greeting.
synopsis: A simple demonstration using a Nix flake to package a Haskell program.
description:
For more information and a tutorial on how to use this package,
please see the README at &lt;https://codeberg.org/mhwombat/hello-flake-haskell#readme&gt;.
@ -3272,10 +3279,11 @@ executable hello-flake-haskell
build-depends:
base,
hostname
-- NOTE: Best practice is to specify version constraints for the packages we depend on.
-- However, I&#39;m confident that this package will only be used as a Nix flake.
-- Nix will automatically ensure that anyone running this program is using the
-- same library versions that I used to build it.
-- NOTE: Best practice is to specify version constraints for the packages we depend on.
-- However, I&#39;m confident that this package will only be used as a Nix flake.
-- Nix will automatically ensure that anyone running this program is using the
-- same library versions that I used to build it.
default-language: Haskell2010
</pre></div></td></tr></table></div></code></pre>
</div>
</div>
@ -3293,7 +3301,7 @@ and problems in your Cabal file.</p>
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ cabal build
sh: line 35: cabal: command not found</pre>
sh: line 40: cabal: command not found</pre>
</div>
</div>
<div class="paragraph">
@ -3305,23 +3313,17 @@ Rather than launch another shell-within-a-shell, let&#8217;s exit create a new o
<pre class="nowrap">$ exit
$ nix-shell -p "[ cabal-install (haskellPackages.ghcWithPackages (pkgs: with pkgs; [ hostname ]))]"
$ cabal build
Warning: The package list for 'hackage.haskell.org' is 24 days old.
Run 'cabal update' to get the latest list of available packages.
Resolving dependencies...
Build profile: -w ghc-9.4.8 -O1
Build profile: -w ghc-9.8.4 -O1
In order, the following will be built (use -v for more details):
- hello-flake-haskell-1.0.0 (exe:hello-flake-haskell) (first run)
Configuring executable 'hello-flake-haskell' for hello-flake-haskell-1.0.0..
Warning: Packages using 'cabal-version: &gt;= 1.10' and before 'cabal-version:
3.4' must specify the 'default-language' field for each component (e.g.
Haskell98 or Haskell2010). If a component uses different languages in
different modules then list the other ones in the 'other-languages' field.
Warning: The 'license-file' field refers to the file 'LICENSE' which does not
exist.
Preprocessing executable 'hello-flake-haskell' for hello-flake-haskell-1.0.0..
Building executable 'hello-flake-haskell' for hello-flake-haskell-1.0.0..
[1 of 1] Compiling Main ( Main.hs, /home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell/dist-newstyle/build/x86_64-linux/ghc-9.4.8/hello-flake-haskell-1.0.0/x/hello-flake-haskell/build/hello-flake-haskell/hello-flake-haskell-tmp/Main.o )
[2 of 2] Linking /home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell/dist-newstyle/build/x86_64-linux/ghc-9.4.8/hello-flake-haskell-1.0.0/x/hello-flake-haskell/build/hello-flake-haskell/hello-flake-haskell
Configuring executable 'hello-flake-haskell' for hello-flake-haskell-1.0.0...
Warning: [unknown-file] The 'license-file' field refers to the file 'LICENSE'
which does not exist.
Preprocessing executable 'hello-flake-haskell' for hello-flake-haskell-1.0.0...
Building executable 'hello-flake-haskell' for hello-flake-haskell-1.0.0...
[1 of 1] Compiling Main ( Main.hs, dist-newstyle/build/x86_64-linux/ghc-9.8.4/hello-flake-haskell-1.0.0/x/hello-flake-haskell/build/hello-flake-haskell/hello-flake-haskell-tmp/Main.o )
[2 of 2] Linking dist-newstyle/build/x86_64-linux/ghc-9.8.4/hello-flake-haskell-1.0.0/x/hello-flake-haskell/build/hello-flake-haskell/hello-flake-haskell
$ cabal run
Hello from Haskell inside a Nix flake!
Your hostname is: wombat11k
@ -3329,7 +3331,7 @@ $ exit</pre>
</div>
</div>
<div class="paragraph">
<p>After a lot of output messages, the build succeeds and the program runs.</p>
<p>After some output messages, the build succeeds and the program runs.</p>
</div>
</div>
<div class="sect3">
@ -3369,26 +3371,26 @@ different are the development shell and the package builder.</p>
<span class="normal">22</span>
<span class="normal">23</span>
<span class="normal">24</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-p">{</span>
<span class="tok-ss">description =</span> <span class="tok-s2">&quot;a flake using Haskell&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">description</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;a flake using Haskell&quot;</span><span class="tok-p">;</span>
<span class="tok-c1"># This example uses haskell-flake to make things simpler.</span>
<span class="tok-c1"># See https://haskell.flake.page/ for more information and examples.</span>
<span class="tok-ss">inputs =</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:nixos/nixpkgs/nixpkgs-unstable&quot;</span><span class="tok-p">;</span>
flake-parts<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:hercules-ci/flake-parts&quot;</span><span class="tok-p">;</span>
haskell-flake<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:srid/haskell-flake&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">inputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:nixos/nixpkgs/nixpkgs-unstable&quot;</span><span class="tok-p">;</span>
flake-parts<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:hercules-ci/flake-parts&quot;</span><span class="tok-p">;</span>
haskell-flake<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:srid/haskell-flake&quot;</span><span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">outputs =</span> inputs<span class="tok-p">@{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-parts<span class="tok-p">,</span> <span class="tok-o">...</span> <span class="tok-p">}:</span>
<span class="tok-ss">outputs</span> <span class="tok-o">=</span> inputs<span class="tok-p">@{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-parts<span class="tok-p">,</span> <span class="tok-o">...</span> <span class="tok-p">}:</span>
flake-parts<span class="tok-o">.</span>lib<span class="tok-o">.</span>mkFlake <span class="tok-p">{</span> <span class="tok-k">inherit</span> inputs<span class="tok-p">;</span> <span class="tok-p">}</span> <span class="tok-p">{</span>
<span class="tok-ss">systems =</span> nixpkgs<span class="tok-o">.</span>lib<span class="tok-o">.</span>systems<span class="tok-o">.</span>flakeExposed<span class="tok-p">;</span>
<span class="tok-ss">imports =</span> <span class="tok-p">[</span> inputs<span class="tok-o">.</span>haskell-flake<span class="tok-o">.</span>flakeModule <span class="tok-p">];</span>
<span class="tok-ss">systems</span> <span class="tok-o">=</span> nixpkgs<span class="tok-o">.</span>lib<span class="tok-o">.</span>systems<span class="tok-o">.</span>flakeExposed<span class="tok-p">;</span>
<span class="tok-ss">imports</span> <span class="tok-o">=</span> <span class="tok-p">[</span> inputs<span class="tok-o">.</span>haskell-flake<span class="tok-o">.</span>flakeModule <span class="tok-p">];</span>
<span class="tok-ss">perSystem =</span> <span class="tok-p">{</span> self&#39;<span class="tok-p">,</span> pkgs<span class="tok-p">,</span> <span class="tok-o">...</span> <span class="tok-p">}:</span> <span class="tok-p">{</span>
haskellProjects<span class="tok-o">.</span><span class="tok-ss">default =</span> <span class="tok-p">{};</span>
<span class="tok-ss">perSystem</span> <span class="tok-o">=</span> <span class="tok-p">{</span> self&#39;<span class="tok-p">,</span> pkgs<span class="tok-p">,</span> <span class="tok-o">...</span> <span class="tok-p">}:</span> <span class="tok-p">{</span>
haskellProjects<span class="tok-o">.</span><span class="tok-ss">default</span> <span class="tok-o">=</span> <span class="tok-p">{};</span>
<span class="tok-c1"># haskell-flake doesn&#39;t set the default package, but you can do it here.</span>
packages<span class="tok-o">.</span><span class="tok-ss">default =</span> self&#39;<span class="tok-o">.</span>packages<span class="tok-o">.</span>hello-flake-haskell<span class="tok-p">;</span>
packages<span class="tok-o">.</span><span class="tok-ss">default</span> <span class="tok-o">=</span> self&#39;<span class="tok-o">.</span>packages<span class="tok-o">.</span>hello-flake-haskell<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-p">};</span>
<span class="tok-p">}</span>
@ -3397,14 +3399,28 @@ different are the development shell and the package builder.</p>
</div>
<div class="paragraph">
<p>The above definition will work for most of your haskell projects;
simply change the <code>description</code> and the package name in <code>packages.default</code>.
Let&#8217;s try out the new flake.</p>
simply change the <code>description</code> and the package name in <code>packages.default</code>.</p>
</div>
<div class="paragraph">
<p>We also need a <code>LICENSE</code> file.
For now, this can be empty.</p>
</div>
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ touch LICENSE</pre>
</div>
</div>
<div class="paragraph">
<p>Let&#8217;s try out the new flake.</p>
</div>
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ nix run
warning: Git tree '/home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell' is dirty
error: getting status of '/nix/store/0ccnxa25whszw7mgbgyzdm4nqc0zwnm8-source/flake.nix': No such file or directory</pre>
error: Path 'flake.nix' in the repository "/home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell" is not tracked by Git.
To make it visible to Nix, run:
git -C "/home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell" add "flake.nix"</pre>
</div>
</div>
<div class="paragraph">
@ -3414,26 +3430,21 @@ repo before building or running the flake.</p>
</div>
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ git add flake.nix hello-flake-haskell.cabal Main.hs
<pre class="nowrap">$ git add flake.nix hello-flake-haskell.cabal LICENSE Main.hs
$ nix run
warning: Git tree '/home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell' is dirty
warning: creating lock file '/home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell/flake.lock'
warning: creating lock file '"/home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell/flake.lock"':
• Added input 'flake-parts':
'github:hercules-ci/flake-parts/af66ad14b28a127c5c0f3bbb298218fc63528a18?narHash=sha256-pHYj8gUBapuUzKV/kN/tR3Zvqc7o6gdFB9XKXIp1SQ8%3D' (2025-08-06)
• Added input 'flake-parts/nixpkgs-lib':
'github:nix-community/nixpkgs.lib/0f36c44e01a6129be94e3ade315a5883f0228a6e?narHash=sha256-zvaMGVn14/Zz8hnp4VWT9xVnhc8vuL3TStRqwk22biA%3D' (2025-07-27)
• Added input 'haskell-flake':
'github:srid/haskell-flake/4bed0d0db1b5ae4e50cf4f1373fdf68d9c070517?narHash=sha256-lsEcVlgd6Xck%2B0pOmtEL93b138Tg8g6xTFg4fZ3YZ30%3D' (2025-08-18)
• Added input 'nixpkgs':
'github:nixos/nixpkgs/a650b5d0de99158323597f048667c4d914243224?narHash=sha256-ixn50x9Qoh9RNpG3LGhTI86GioR9GkGxR4%2Bj/Ttj0uE%3D' (2025-08-15)
warning: Git tree '/home/amy/codeberg/nix-book/source/new-flake/haskell-flake/hello-haskell' is dirty
these 2 derivations will be built:
/nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv
/nix/store/8qdbmfms1h0b60aqdxfk28fmdnlkcm1l-hello-flake-haskell-1.0.0.drv
building '/nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv'...
error: builder for '/nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv' failed with exit code 1;
last 7 log lines:
&gt; unpacking source archive /nix/store/gg6b20p83m5mqcfp1qr0w37bjhz3k33y-source-hello-flake-haskell
&gt; source root is source-hello-flake-haskell
&gt; Config file path source is default config file.
&gt; Config file not found: /build/source-hello-flake-haskell/.config/cabal/config
&gt; Writing default configuration to
&gt; /build/source-hello-flake-haskell/.config/cabal/config
&gt; /build/source-hello-flake-haskell/./LICENSE: withBinaryFile: does not exist (No such file or directory)
For full logs, run 'nix log /nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv'.
error: 1 dependencies of derivation '/nix/store/8qdbmfms1h0b60aqdxfk28fmdnlkcm1l-hello-flake-haskell-1.0.0.drv' failed to build</pre>
Hello from Haskell inside a Nix flake!
Your hostname is: wombat11k</pre>
</div>
</div>
<div class="paragraph">
@ -3446,8 +3457,9 @@ repo, and commit all important files.</p>
<div class="content">
<pre class="nowrap">$ git add flake.lock
$ git commit -a -m 'initial commit'
[master (root-commit) 666b827] initial commit
4 files changed, 137 insertions(+)
[master (root-commit) a370ad5] initial commit
5 files changed, 136 insertions(+)
create mode 100644 LICENSE
create mode 100644 Main.hs
create mode 100644 flake.lock
create mode 100644 flake.nix
@ -3462,21 +3474,8 @@ another directory and running it from there.</p>
<div class="content">
<pre class="nowrap">$ cd ..
$ nix run ./hello-haskell
these 2 derivations will be built:
/nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv
/nix/store/8qdbmfms1h0b60aqdxfk28fmdnlkcm1l-hello-flake-haskell-1.0.0.drv
building '/nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv'...
error: builder for '/nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv' failed with exit code 1;
last 7 log lines:
&gt; unpacking source archive /nix/store/gg6b20p83m5mqcfp1qr0w37bjhz3k33y-source-hello-flake-haskell
&gt; source root is source-hello-flake-haskell
&gt; Config file path source is default config file.
&gt; Config file not found: /build/source-hello-flake-haskell/.config/cabal/config
&gt; Writing default configuration to
&gt; /build/source-hello-flake-haskell/.config/cabal/config
&gt; /build/source-hello-flake-haskell/./LICENSE: withBinaryFile: does not exist (No such file or directory)
For full logs, run 'nix log /nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv'.
error: 1 dependencies of derivation '/nix/store/8qdbmfms1h0b60aqdxfk28fmdnlkcm1l-hello-flake-haskell-1.0.0.drv' failed to build</pre>
Hello from Haskell inside a Nix flake!
Your hostname is: wombat11k</pre>
</div>
</div>
<div class="paragraph">
@ -3631,7 +3630,7 @@ package manually.</p>
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ python -m build
/nix/store/qp5zys77biz7imbk6yy85q5pdv7qk84j-python3-3.11.6/bin/python: No module named build</pre>
/nix/store/9yh9ak97gn659bk4d3n411fx6c0ng7s2-python3-3.13.5/bin/python: No module named build</pre>
</div>
</div>
<div class="paragraph">
@ -3777,23 +3776,23 @@ something like this.</p>
<span class="tok-c1"># See https://github.com/mhwombat/nix-for-numbskulls/blob/main/flakes.md</span>
<span class="tok-c1"># for a brief overview of what each section in a flake should or can contain.</span>
<span class="tok-ss">description =</span> <span class="tok-s2">&quot;a very simple and friendly flake written in Python&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">description</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;a very simple and friendly flake written in Python&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">inputs =</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url =</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">inputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span>
nixpkgs<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:NixOS/nixpkgs&quot;</span><span class="tok-p">;</span>
flake-utils<span class="tok-o">.</span><span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;github:numtide/flake-utils&quot;</span><span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">outputs =</span> <span class="tok-p">{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-utils <span class="tok-p">}:</span>
<span class="tok-ss">outputs</span> <span class="tok-o">=</span> <span class="tok-p">{</span> self<span class="tok-p">,</span> nixpkgs<span class="tok-p">,</span> flake-utils <span class="tok-p">}:</span>
flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>eachDefaultSystem <span class="tok-p">(</span>system<span class="tok-p">:</span>
<span class="tok-k">let</span>
<span class="tok-ss">pkgs =</span> <span class="tok-nb">import</span> nixpkgs <span class="tok-p">{</span> <span class="tok-k">inherit</span> system<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">python =</span> pkgs<span class="tok-o">.</span>python3<span class="tok-p">;</span>
<span class="tok-ss">pkgs</span> <span class="tok-o">=</span> <span class="tok-nb">import</span> nixpkgs <span class="tok-p">{</span> <span class="tok-k">inherit</span> system<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">python</span> <span class="tok-o">=</span> pkgs<span class="tok-o">.</span>python3<span class="tok-p">;</span>
<span class="tok-k">in</span>
<span class="tok-p">{</span>
<span class="tok-ss">devShells =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">default =</span> pkgs<span class="tok-o">.</span>mkShell <span class="tok-p">{</span>
<span class="tok-ss">packages =</span> <span class="tok-p">[</span>
<span class="tok-ss">devShells</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">default</span> <span class="tok-o">=</span> pkgs<span class="tok-o">.</span>mkShell <span class="tok-p">{</span>
<span class="tok-ss">packages</span> <span class="tok-o">=</span> <span class="tok-p">[</span>
<span class="tok-c1"># Python plus helper tools</span>
<span class="tok-p">(</span>python<span class="tok-o">.</span>withPackages <span class="tok-p">(</span>ps<span class="tok-p">:</span> <span class="tok-k">with</span> ps<span class="tok-p">;</span> <span class="tok-p">[</span>
virtualenv <span class="tok-c1"># Virtualenv</span>
@ -3803,20 +3802,20 @@ something like this.</p>
<span class="tok-p">};</span>
<span class="tok-p">};</span>
<span class="tok-ss">packages =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello =</span> python<span class="tok-o">.</span>pkgs<span class="tok-o">.</span>buildPythonApplication <span class="tok-p">{</span>
<span class="tok-ss">name =</span> <span class="tok-s2">&quot;hello-flake-python&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">buildInputs =</span> <span class="tok-k">with</span> python<span class="tok-o">.</span>pkgs<span class="tok-p">;</span> <span class="tok-p">[</span> pip <span class="tok-p">];</span>
<span class="tok-ss">src =</span> <span class="tok-o">.</span><span class="tok-l">/.</span><span class="tok-p">;</span>
<span class="tok-ss">packages</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello</span> <span class="tok-o">=</span> python<span class="tok-o">.</span>pkgs<span class="tok-o">.</span>buildPythonApplication <span class="tok-p">{</span>
<span class="tok-ss">name</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;hello-flake-python&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">buildInputs</span> <span class="tok-o">=</span> <span class="tok-k">with</span> python<span class="tok-o">.</span>pkgs<span class="tok-p">;</span> <span class="tok-p">[</span> pip <span class="tok-p">];</span>
<span class="tok-ss">src</span> <span class="tok-o">=</span> <span class="tok-l">./.</span><span class="tok-p">;</span>
<span class="tok-ss">pyproject</span> <span class="tok-o">=</span> <span class="tok-no">true</span><span class="tok-p">;</span>
<span class="tok-ss">build-system</span> <span class="tok-o">=</span> <span class="tok-k">with</span> python<span class="tok-o">.</span>pkgs<span class="tok-p">;</span> <span class="tok-p">[</span> setuptools <span class="tok-p">];</span>
<span class="tok-p">};</span>
<span class="tok-ss">default =</span> hello<span class="tok-p">;</span>
<span class="tok-ss">default</span> <span class="tok-o">=</span> hello<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-ss">apps =</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello =</span> flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>mkApp <span class="tok-p">{</span> <span class="tok-ss">drv =</span> self<span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-err">$</span><span class="tok-p">{</span>system<span class="tok-p">}</span><span class="tok-o">.</span>hello<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">default =</span> hello<span class="tok-p">;</span>
<span class="tok-ss">apps</span> <span class="tok-o">=</span> <span class="tok-k">rec</span> <span class="tok-p">{</span>
<span class="tok-ss">hello</span> <span class="tok-o">=</span> flake-utils<span class="tok-o">.</span>lib<span class="tok-o">.</span>mkApp <span class="tok-p">{</span> <span class="tok-ss">drv</span> <span class="tok-o">=</span> self<span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-si">${</span>system<span class="tok-si">}</span><span class="tok-o">.</span>hello<span class="tok-p">;</span> <span class="tok-p">};</span>
<span class="tok-ss">default</span> <span class="tok-o">=</span> hello<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-p">}</span>
<span class="tok-p">);</span>
@ -3830,8 +3829,11 @@ something like this.</p>
<div class="literalblock">
<div class="content">
<pre class="nowrap">$ nix run
warning: Git tree '/home/amy/codeberg/nix-book/source/new-flake/python-flake/hello-python' is dirty
error: getting status of '/nix/store/0ccnxa25whszw7mgbgyzdm4nqc0zwnm8-source/flake.nix': No such file or directory</pre>
error: Path 'flake.nix' in the repository "/home/amy/codeberg/nix-book/source/new-flake/python-flake/hello-python" is not tracked by Git.
To make it visible to Nix, run:
git -C "/home/amy/codeberg/nix-book/source/new-flake/python-flake/hello-python" add "flake.nix"</pre>
</div>
</div>
<div class="paragraph">
@ -3844,8 +3846,17 @@ repo before building or running the flake.</p>
<pre class="nowrap">$ git add flake.nix setup.py hello.py
$ nix run
warning: Git tree '/home/amy/codeberg/nix-book/source/new-flake/python-flake/hello-python' is dirty
warning: creating lock file '/home/amy/codeberg/nix-book/source/new-flake/python-flake/hello-python/flake.lock'
warning: creating lock file '"/home/amy/codeberg/nix-book/source/new-flake/python-flake/hello-python/flake.lock"':
• Added input 'flake-utils':
'github:numtide/flake-utils/11707dc2f618dd54ca8739b309ec4fc024de578b?narHash=sha256-l0KFg5HjrsfsO/JpG%2Br7fRrqm12kzFHyUHqHCVpMMbI%3D' (2024-11-13)
• Added input 'flake-utils/systems':
'github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e?narHash=sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768%3D' (2023-04-09)
• Added input 'nixpkgs':
'github:NixOS/nixpkgs/375ab11873f71477e1e9afc240dd815d00ce05bf?narHash=sha256-WB8bx4RyG1hjt49/yafemlpImojvq/vWpVQFW0/DVjI%3D' (2025-08-19)
warning: Git tree '/home/amy/codeberg/nix-book/source/new-flake/python-flake/hello-python' is dirty
this derivation will be built:
/nix/store/vnwhjlij3k1lkqxjyznh78xbsns9rpqy-hello-flake-python.drv
building '/nix/store/vnwhjlij3k1lkqxjyznh78xbsns9rpqy-hello-flake-python.drv'...
Hello from inside a Python program built with a Nix flake!</pre>
</div>
</div>
@ -3859,7 +3870,7 @@ repo, and commit all important files.</p>
<div class="content">
<pre class="nowrap">$ git add flake.lock
$ git commit -a -m 'initial commit'
[master (root-commit) ddb5606] initial commit
[master (root-commit) 5e2c858] initial commit
4 files changed, 127 insertions(+)
create mode 100644 flake.lock
create mode 100644 flake.nix
@ -3875,6 +3886,9 @@ another directory and running it from there.</p>
<div class="content">
<pre class="nowrap">$ cd ..
$ nix run ./hello-python
this derivation will be built:
/nix/store/m96s3wx0wghysihixgv2vldfwx4zwwqb-hello-flake-python.drv
building '/nix/store/m96s3wx0wghysihixgv2vldfwx4zwwqb-hello-flake-python.drv'...
Hello from inside a Python program built with a Nix flake!</pre>
</div>
</div>
@ -3969,7 +3983,7 @@ $ cowsay "moo"
<span class="normal">6</span>
<span class="normal">7</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-k">with</span> <span class="tok-p">(</span><span class="tok-nb">import</span> <span class="tok-l">&lt;nixpkgs&gt;</span> <span class="tok-p">{});</span>
mkShell <span class="tok-p">{</span>
<span class="tok-ss">buildInputs =</span> <span class="tok-p">[</span>
<span class="tok-ss">buildInputs</span> <span class="tok-o">=</span> <span class="tok-p">[</span>
hello
cowsay
<span class="tok-p">];</span>
@ -4052,13 +4066,13 @@ modify the URL.</p>
<span class="normal"> 9</span>
<span class="normal">10</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-k">with</span> <span class="tok-p">(</span><span class="tok-nb">import</span> <span class="tok-l">&lt;nixpkgs&gt;</span> <span class="tok-p">{});</span>
<span class="tok-k">let</span>
<span class="tok-ss">hello-nix =</span> <span class="tok-nb">import</span> <span class="tok-p">(</span><span class="tok-nb">builtins</span><span class="tok-o">.</span>fetchGit <span class="tok-p">{</span>
<span class="tok-ss">url =</span> <span class="tok-s2">&quot;https://codeberg.org/mhwombat/hello-nix&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">rev =</span> <span class="tok-s2">&quot;aa2c87f8b89578b069b09fdb2be30a0c9d8a77d8&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">hello-nix</span> <span class="tok-o">=</span> <span class="tok-nb">import</span> <span class="tok-p">(</span><span class="tok-nb">builtins</span><span class="tok-o">.</span>fetchGit <span class="tok-p">{</span>
<span class="tok-ss">url</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;https://codeberg.org/mhwombat/hello-nix&quot;</span><span class="tok-p">;</span>
<span class="tok-ss">rev</span> <span class="tok-o">=</span> <span class="tok-s2">&quot;aa2c87f8b89578b069b09fdb2be30a0c9d8a77d8&quot;</span><span class="tok-p">;</span>
<span class="tok-p">});</span>
<span class="tok-k">in</span>
mkShell <span class="tok-p">{</span>
<span class="tok-ss">buildInputs =</span> <span class="tok-p">[</span> hello-nix <span class="tok-p">];</span>
<span class="tok-ss">buildInputs</span> <span class="tok-o">=</span> <span class="tok-p">[</span> hello-nix <span class="tok-p">];</span>
<span class="tok-p">}</span>
</pre></div></td></tr></table></div></code></pre>
</div>
@ -4100,12 +4114,12 @@ modify the URL.</p>
<span class="normal">10</span>
<span class="normal">11</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-k">with</span> <span class="tok-p">(</span><span class="tok-nb">import</span> <span class="tok-l">&lt;nixpkgs&gt;</span> <span class="tok-p">{});</span>
<span class="tok-k">let</span>
<span class="tok-ss">hello-flake =</span> <span class="tok-p">(</span> <span class="tok-nb">builtins</span><span class="tok-o">.</span>getFlake
<span class="tok-ss">hello-flake</span> <span class="tok-o">=</span> <span class="tok-p">(</span> <span class="tok-nb">builtins</span><span class="tok-o">.</span>getFlake
<span class="tok-l">git+https://codeberg.org/mhwombat/hello-flake?ref=main&amp;rev=3aa43dbe7be878dde7b2bdcbe992fe1705da3150</span>
<span class="tok-p">)</span><span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-err">$</span><span class="tok-p">{</span><span class="tok-nb">builtins</span><span class="tok-o">.</span>currentSystem<span class="tok-p">}</span><span class="tok-o">.</span>default<span class="tok-p">;</span>
<span class="tok-p">)</span><span class="tok-o">.</span>packages<span class="tok-o">.</span><span class="tok-si">${</span><span class="tok-nb">builtins</span><span class="tok-o">.</span>currentSystem<span class="tok-si">}</span><span class="tok-o">.</span>default<span class="tok-p">;</span>
<span class="tok-k">in</span>
mkShell <span class="tok-p">{</span>
<span class="tok-ss">buildInputs =</span> <span class="tok-p">[</span>
<span class="tok-ss">buildInputs</span> <span class="tok-o">=</span> <span class="tok-p">[</span>
hello-flake
<span class="tok-p">];</span>
<span class="tok-p">}</span>
@ -4148,10 +4162,10 @@ but you don&#8217;t want to bother writing a cabal file.</p>
<span class="normal">8</span>
<span class="normal">9</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-k">with</span> <span class="tok-p">(</span><span class="tok-nb">import</span> <span class="tok-l">&lt;nixpkgs&gt;</span> <span class="tok-p">{});</span>
<span class="tok-k">let</span>
<span class="tok-ss">customGhc =</span> haskellPackages<span class="tok-o">.</span>ghcWithPackages <span class="tok-p">(</span>pkgs<span class="tok-p">:</span> <span class="tok-k">with</span> pkgs<span class="tok-p">;</span> <span class="tok-p">[</span> containers <span class="tok-p">]);</span>
<span class="tok-ss">customGhc</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>ghcWithPackages <span class="tok-p">(</span>pkgs<span class="tok-p">:</span> <span class="tok-k">with</span> pkgs<span class="tok-p">;</span> <span class="tok-p">[</span> containers <span class="tok-p">]);</span>
<span class="tok-k">in</span>
mkShell <span class="tok-p">{</span>
<span class="tok-ss">buildInputs =</span> <span class="tok-p">[</span>
<span class="tok-ss">buildInputs</span> <span class="tok-o">=</span> <span class="tok-p">[</span>
customGhc
<span class="tok-p">];</span>
<span class="tok-p">}</span>
@ -4271,12 +4285,12 @@ that are on my hard drive.</p>
<span class="normal">13</span>
<span class="normal">14</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-k">with</span> <span class="tok-p">(</span><span class="tok-nb">import</span> <span class="tok-l">&lt;nixpkgs&gt;</span> <span class="tok-p">{});</span>
<span class="tok-k">let</span>
<span class="tok-ss">pandoc-linear-table =</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-linear-table&quot;</span> <span class="tok-l">/home/amy/github/pandoc-linear-table</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-logic-proof =</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-logic-proof&quot;</span> <span class="tok-l">/home/amy/github/pandoc-logic-proof</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-columns =</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-columns&quot;</span> <span class="tok-l">/home/amy/github/pandoc-columns</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-linear-table</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-linear-table&quot;</span> <span class="tok-l">/home/amy/github/pandoc-linear-table</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-logic-proof</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-logic-proof&quot;</span> <span class="tok-l">/home/amy/github/pandoc-logic-proof</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-columns</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-columns&quot;</span> <span class="tok-l">/home/amy/github/pandoc-columns</span> <span class="tok-p">{};</span>
<span class="tok-k">in</span>
mkShell <span class="tok-p">{</span>
<span class="tok-ss">buildInputs =</span> <span class="tok-p">[</span>
<span class="tok-ss">buildInputs</span> <span class="tok-o">=</span> <span class="tok-p">[</span>
pandoc
pandoc-linear-table
pandoc-logic-proof
@ -4321,16 +4335,16 @@ The fourth package depends on the first three to build.</p>
<span class="normal">18</span>
<span class="normal">19</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-k">with</span> <span class="tok-p">(</span><span class="tok-nb">import</span> <span class="tok-l">&lt;nixpkgs&gt;</span> <span class="tok-p">{});</span>
<span class="tok-k">let</span>
<span class="tok-ss">pandoc-linear-table =</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-linear-table&quot;</span> <span class="tok-l">/home/amy/github/pandoc-linear-table</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-logic-proof =</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-logic-proof&quot;</span> <span class="tok-l">/home/amy/github/pandoc-logic-proof</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-columns =</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-columns&quot;</span> <span class="tok-l">/home/amy/github/pandoc-columns</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-maths-web =</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-maths-web&quot;</span> <span class="tok-l">/home/amy/github/pandoc-maths-web</span>
<span class="tok-ss">pandoc-linear-table</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-linear-table&quot;</span> <span class="tok-l">/home/amy/github/pandoc-linear-table</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-logic-proof</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-logic-proof&quot;</span> <span class="tok-l">/home/amy/github/pandoc-logic-proof</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-columns</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-columns&quot;</span> <span class="tok-l">/home/amy/github/pandoc-columns</span> <span class="tok-p">{};</span>
<span class="tok-ss">pandoc-maths-web</span> <span class="tok-o">=</span> haskellPackages<span class="tok-o">.</span>callCabal2nix <span class="tok-s2">&quot;pandoc-maths-web&quot;</span> <span class="tok-l">/home/amy/github/pandoc-maths-web</span>
<span class="tok-p">{</span>
<span class="tok-k">inherit</span> pandoc-linear-table pandoc-logic-proof pandoc-columns<span class="tok-p">;</span>
<span class="tok-p">};</span>
<span class="tok-k">in</span>
mkShell <span class="tok-p">{</span>
<span class="tok-ss">buildInputs =</span> <span class="tok-p">[</span>
<span class="tok-ss">buildInputs</span> <span class="tok-o">=</span> <span class="tok-p">[</span>
pandoc
pandoc-linear-table
pandoc-logic-proof
@ -4407,9 +4421,9 @@ sanitized: &lt;strong&gt;some text&lt;/strong&gt;</pre>
<span class="normal">5</span>
<span class="normal">6</span></pre></div></td><td class="code"><div><pre><span></span><span class="tok-k">with</span> <span class="tok-p">(</span><span class="tok-nb">import</span> <span class="tok-l">&lt;nixpkgs&gt;</span> <span class="tok-p">{});</span>
mkShell <span class="tok-p">{</span>
<span class="tok-ss">shellHook =</span> <span class="tok-s1">&#39;&#39;</span>
<span class="tok-s1"> export FOO=&quot;bar&quot;</span>
<span class="tok-s1"> &#39;&#39;</span><span class="tok-p">;</span>
<span class="tok-ss">shellHook</span> <span class="tok-o">=</span> <span class="tok-s tok-s-Multiline">&#39;&#39;</span>
<span class="tok-s tok-s-Multiline"> export FOO=&quot;bar&quot;</span>
<span class="tok-s tok-s-Multiline"> &#39;&#39;</span><span class="tok-p">;</span>
<span class="tok-p">}</span>
</pre></div></td></tr></table></div></code></pre>
</div>
@ -4430,7 +4444,7 @@ mkShell <span class="tok-p">{</span>
</div>
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Last updated 2024-04-25 15:41:01 IST
Last updated 2025-08-19 21:27:18 IST
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0
source/new-flake/haskell-flake/main.adoc
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@ -129,6 +129,11 @@ $ runghc Main.hs
Success! Now we know the program works.
....
$# echo '$ exit'
....
== The cabal file
It's time to write a Cabal file for this program.
@ -170,7 +175,7 @@ $ cabal run
$# echo '$ exit'
....
After a lot of output messages, the build succeeds and the program runs.
After some output messages, the build succeeds and the program runs.
== The Nix flake
@ -192,6 +197,14 @@ $# cat flake.nix
The above definition will work for most of your haskell projects;
simply change the `description` and the package name in `packages.default`.
We also need a `LICENSE` file.
For now, this can be empty.
....
$ touch LICENSE
....
Let's try out the new flake.
....
@ -203,7 +216,7 @@ part of the repository. We need to add all of the important files to the
repo before building or running the flake.
....
$ git add flake.nix hello-flake-haskell.cabal Main.hs
$ git add flake.nix hello-flake-haskell.cabal LICENSE Main.hs
$ nix run
....

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wombats-book-of-nix.pdf
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