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OCaml News 2023/5/9
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May 9, 2023
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<h1 id="二〇二三年五月六日-二〇二三年五月九日"><a href="#二〇二三年五月六日-二〇二三年五月九日" class="headerlink" title="二〇二三年五月六日 - 二〇二三年五月九日"></a>二〇二三年五月六日 - 二〇二三年五月九日</h1><h2 id="在Eio中不使用Unix和Sys模块实现所有I-x2F-O和文件系统操作?"><a href="#在Eio中不使用Unix和Sys模块实现所有I-x2F-O和文件系统操作?" class="headerlink" title="在Eio中不使用Unix和Sys模块实现所有I/O和文件系统操作?"></a>在Eio中不使用Unix和Sys模块实现所有I/O和文件系统操作?</h2><blockquote>
<p>EIO: <a target="_blank" rel="noopener" href="https://github.com/ocaml-multicore/eio">Effects-based direct-style IO for multicore OCaml</a></p>
</blockquote>
<p>例如<code>Sys.is_directory</code>, <code>Sys.file_exists</code>,<code>Sys.is_regular_file</code>这些函数在Eio中并没有相关的实现, 因为Eio目前还缺少很多文件操作的实现: <a target="_blank" rel="noopener" href="https://github.com/ocaml-multicore/eio/issues/510">Add missing file operations #510</a>。</p>
<p>但退一步,如果需要,可以用 <code>Eio_unix.run_in_systhread</code>来运行Unix的相关操作从而不阻塞Eio线程。</p>
<p>关于执行外部命令, 例如<code>Sys.command</code>或<code>Unix.create_process</code>函数, 在Eio中可以通过<code>Eio.Process</code>模块实现,例如:</p>
<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"># <span class="type">Eio_main</span>.run @@ <span class="keyword">fun</span> env -></span><br><span class="line"> <span class="keyword">let</span> proc_mgr = <span class="type">Eio</span>.<span class="type">Stdenv</span>.process_mgr env <span class="keyword">in</span></span><br><span class="line"> <span class="type">Eio</span>.<span class="type">Process</span>.run proc_mgr [<span class="string">"echo"</span>; <span class="string">"hello"</span>];;</span><br><span class="line">hello</span><br><span class="line">- : <span class="built_in">unit</span> = <span class="literal">()</span></span><br></pre></td></tr></table></figure>
<p>相关文档: <a target="_blank" rel="noopener" href="https://github.com/ocaml-multicore/eio#running-processes">https://github.com/ocaml-multicore/eio#running-processes</a></p>
<p>论坛原帖:<a target="_blank" rel="noopener" href="https://discuss.ocaml.org/t/what-are-equivalent-to-some-sys-functions-in-eio-and-other-eio-questions/12126">https://discuss.ocaml.org/t/what-are-equivalent-to-some-sys-functions-in-eio-and-other-eio-questions/12126</a></p>
<h2 id="为一个现有的Dune项目生成最小的mli文件"><a href="#为一个现有的Dune项目生成最小的mli文件" class="headerlink" title="为一个现有的Dune项目生成最小的mli文件"></a>为一个现有的Dune项目生成最小的mli文件</h2><blockquote>
<p>Reanalyze: <a target="_blank" rel="noopener" href="https://github.com/rescript-association/reanalyze">Experimental analyses for ReScript and OCaml: globally dead values/types, exception analysis, and termination analysis.</a></p>
</blockquote>
<p>reanalyze可以分析项目中的dead code, 它并不能直接实现这个需求, 但可能可以利用这些信息对实施相关分析提供一个良好的起点。</p>
<p>论坛原帖: <a target="_blank" rel="noopener" href="https://discuss.ocaml.org/t/how-to-create-the-minimal-mli-files-using-dune/12115">https://discuss.ocaml.org/t/how-to-create-the-minimal-mli-files-using-dune/12115</a></p>
<h2 id="自动派生枚举转换函数"><a href="#自动派生枚举转换函数" class="headerlink" title="自动派生枚举转换函数"></a>自动派生枚举转换函数</h2><p>主要想实现的是自动生成如下代码中的 <code>_foo</code> 和 <code>_bar</code> 函数。 也就是将具有无参数constructors的variant视为enum,并为每个constructor映射一个整数值:</p>
<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">type</span> my_enum = <span class="type">A</span> | <span class="type">B</span> | <span class="type">C</span> | <span class="type">D</span> | <span class="type">E</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> _foo (x : my_enum) : <span class="built_in">int</span> =</span><br><span class="line"> <span class="keyword">match</span> x <span class="keyword">with</span></span><br><span class="line"> | <span class="type">A</span> -> <span class="number">0</span></span><br><span class="line"> | <span class="type">B</span> -> <span class="number">1</span></span><br><span class="line"> | <span class="type">C</span> -> <span class="number">2</span></span><br><span class="line"> | <span class="type">D</span> -> <span class="number">3</span></span><br><span class="line"> | <span class="type">E</span> -> <span class="number">4</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> _bar (n : <span class="built_in">int</span>) : my_enum =</span><br><span class="line"> <span class="keyword">match</span> n <span class="keyword">with</span></span><br><span class="line"> | <span class="number">0</span> -> <span class="type">A</span></span><br><span class="line"> | <span class="number">1</span> -> <span class="type">B</span></span><br><span class="line"> | <span class="number">2</span> -> <span class="type">C</span></span><br><span class="line"> | <span class="number">3</span> -> <span class="type">D</span></span><br><span class="line"> | <span class="number">4</span> -> <span class="type">E</span></span><br><span class="line"> | _ -> failwith <span class="string">"not handled"</span></span><br></pre></td></tr></table></figure>
<p><code>ppx_deriving</code>有enum deriver, 可以实现,例如</p>
<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"># <span class="keyword">type</span> insn = <span class="type">Const</span> | <span class="type">Push</span> | <span class="type">Pop</span> | <span class="type">Add</span> [@@deriving enum];;</span><br><span class="line"><span class="keyword">type</span> insn = <span class="type">Const</span> | <span class="type">Push</span> | <span class="type">Pop</span> | <span class="type">Add</span></span><br><span class="line"><span class="keyword">val</span> insn_to_enum : insn -> <span class="built_in">int</span> = <<span class="keyword">fun</span>></span><br><span class="line"><span class="keyword">val</span> insn_of_enum : <span class="built_in">int</span> -> insn option = <<span class="keyword">fun</span>></span><br><span class="line"><span class="keyword">val</span> min_insn : <span class="built_in">int</span> = <span class="number">0</span></span><br><span class="line"><span class="keyword">val</span> max_insn : <span class="built_in">int</span> = <span class="number">3</span></span><br><span class="line"># insn_to_enum <span class="type">Pop</span>;;</span><br><span class="line">- : <span class="built_in">int</span> = <span class="number">2</span></span><br><span class="line"># insn_of_enum <span class="number">3</span>;;</span><br><span class="line">- : insn option = <span class="type">Some</span> <span class="type">Add</span></span><br></pre></td></tr></table></figure>
<p>相关文档: <a target="_blank" rel="noopener" href="https://github.com/ocaml-ppx/ppx_deriving#plugin-enum">https://github.com/ocaml-ppx/ppx_deriving#plugin-enum</a></p>
<p>论坛原帖: <a target="_blank" rel="noopener" href="https://discuss.ocaml.org/t/auto-derive-enum-conversions/12119">https://discuss.ocaml.org/t/auto-derive-enum-conversions/12119</a></p>
<h2 id="在Linux上编译OCaml程序,-在FreeBSD上跑"><a href="#在Linux上编译OCaml程序,-在FreeBSD上跑" class="headerlink" title="在Linux上编译OCaml程序, 在FreeBSD上跑"></a>在Linux上编译OCaml程序, 在FreeBSD上跑</h2><blockquote>
<p>以Linux和FreeBSD都在x86-64架构上运行为例</p>
</blockquote>
<p>如果程序是纯OCaml(没有C bindings之类的),那么只要目标系统中有OCaml解释器(ocamlrun), ocamlc生成的字节码就可以运行, 如果不是的话…</p>
<p>从Linux x86-64到FreeBSD x86-64从表面上看似乎没有太大的困难。 如果知道怎么配置Linux到FreeBSD的交叉编译器(最好使用clang和FreeBSD sysroot),并且愿意维护交叉编译器,<br>可以联系<a target="_blank" rel="noopener" href="https://discuss.ocaml.org/u/jbeckford">jbeckford</a>,他愿意合作将其添加到<code>dkml-base-compiler.4.14.x</code>中。</p>
<p>相关阅读: <a target="_blank" rel="noopener" href="https://docs.freebsd.org/en/books/handbook/linuxemu/">Linux的二进制兼容性</a></p>
<p>论坛原帖: <a target="_blank" rel="noopener" href="https://discuss.ocaml.org/t/how-to-compile-ocaml-program-on-linux-for-running-on-freebsd/12110">https://discuss.ocaml.org/t/how-to-compile-ocaml-program-on-linux-for-running-on-freebsd/12110</a></p>
<h2 id="OCaml的速度竞赛"><a href="#OCaml的速度竞赛" class="headerlink" title="OCaml的速度竞赛"></a>OCaml的速度竞赛</h2><blockquote>
<p>speed-comparison: <a target="_blank" rel="noopener" href="https://github.com/niklas-heer/speed-comparison">A repo which compares the speed of different programming languages</a></p>
</blockquote>
<p>这里用OCaml实现了莱布尼茨算法用于计算圆周率:</p>
<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">(* ocamlopt -O2 -o leibniz leibniz.ml && strip leibniz *)</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> <span class="keyword">rec</span> calc sum curr upto =</span><br><span class="line"> <span class="keyword">if</span> curr >= upto <span class="keyword">then</span> sum</span><br><span class="line"> <span class="keyword">else</span> calc (sum +. <span class="number">1.</span> /. float_of_int curr) (curr + <span class="number">4</span>) upto</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> calc rounds =</span><br><span class="line"> <span class="keyword">let</span> double = rounds * <span class="number">2</span> <span class="keyword">in</span></span><br><span class="line"> calc <span class="number">0.</span> (<span class="number">1</span> - double) (double + <span class="number">1</span>)</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> <span class="literal">()</span> =</span><br><span class="line"> <span class="keyword">let</span> rounds_txt = open_in_bin <span class="string">"rounds.txt"</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> rounds = int_of_string (input_line rounds_txt) <span class="keyword">in</span></span><br><span class="line"> close_in rounds_txt;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">let</span> pi = <span class="number">4.</span> *. calc rounds <span class="keyword">in</span></span><br><span class="line"> <span class="type">Printf</span>.printf <span class="string">"%.16f\n"</span> pi</span><br></pre></td></tr></table></figure>
<p>但性能:</p>
<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">$ time ./leibniz</span><br><span class="line"><span class="number">3.1415926435899633</span></span><br><span class="line">./leibniz <span class="number">0.38</span>s user <span class="number">0.00</span>s system <span class="number">99</span>% cpu <span class="number">0.388</span> total</span><br></pre></td></tr></table></figure>
<p>比Go版本:</p>
<figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">time ./leibniz_go</span><br><span class="line"><span class="number">3.141592663589326</span></span><br><span class="line">./leibniz_go <span class="number">0.13</span>s user <span class="number">0.01</span>s system <span class="number">95</span>% cpu <span class="number">0.142</span> total</span><br></pre></td></tr></table></figure>
<p>慢了很多, 这是因为从生成的<a target="_blank" rel="noopener" href="https://godbolt.org/z/xWrTxa3ov">汇编代码</a>来看, OCaml编译器无法在递归调用中unbox浮点数用于返回值。而命令式版本:</p>
<figure class="highlight ocaml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> calc rounds =</span><br><span class="line"> <span class="keyword">let</span> sum = <span class="built_in">ref</span> <span class="number">0.</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> curr = <span class="built_in">ref</span> (<span class="number">1</span> - rounds * <span class="number">2</span>) <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">for</span> _ = <span class="number">0</span> <span class="keyword">to</span> rounds - <span class="number">1</span> <span class="keyword">do</span></span><br><span class="line"> sum := !sum +. <span class="number">1.</span> /. float_of_int !curr;</span><br><span class="line"> curr := !curr + <span class="number">4</span>;</span><br><span class="line"> <span class="keyword">done</span>;</span><br><span class="line"> !sum</span><br><span class="line"></span><br><span class="line"><span class="keyword">let</span> <span class="literal">()</span> =</span><br><span class="line"> <span class="keyword">let</span> rounds_txt = open_in_bin <span class="string">"rounds.txt"</span> <span class="keyword">in</span></span><br><span class="line"> <span class="keyword">let</span> rounds = int_of_string (input_line rounds_txt) <span class="keyword">in</span></span><br><span class="line"> close_in rounds_txt;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">let</span> pi = <span class="number">4.</span> *. calc rounds <span class="keyword">in</span></span><br><span class="line"> <span class="type">Printf</span>.printf <span class="string">"%.16f\n"</span> pi</span><br></pre></td></tr></table></figure>
<p>的性能将会好得多(<a target="_blank" rel="noopener" href="https://godbolt.org/z/sW46nh1GK">对应的汇编</a>)</p>
<p>所以为了使数字运算的OCaml代码运行得更快,应该避免递归调用(这会抑制unbox浮点值)。</p>
<p>论坛原帖:<a target="_blank" rel="noopener" href="https://discuss.ocaml.org/t/ocaml-speed-comparison-calculating-pi-with-leibniz-optimize/12112">https://discuss.ocaml.org/t/ocaml-speed-comparison-calculating-pi-with-leibniz-optimize/12112</a></p>
<hr>
<h2 id="一些库"><a href="#一些库" class="headerlink" title="一些库"></a>一些库</h2><ul>
<li>OCaml PPX deriver for reflection : <a target="_blank" rel="noopener" href="https://github.com/thierry-martinez/refl">https://github.com/thierry-martinez/refl</a></li>
<li>LexiFi runtime types : <a target="_blank" rel="noopener" href="https://github.com/LexiFi/lrt">https://github.com/LexiFi/lrt</a></li>
<li>Auto generation of idiomatic bindings between Reason and JavaScript: either vanilla or typed with TypeScript/FlowType : <a target="_blank" rel="noopener" href="https://github.com/rescript-association/genType">https://github.com/rescript-association/genType</a></li>
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