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<h1 class="title">Customizing the prompt buffer</h1>
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<p class="author">By Pierre Neidhardt</p>
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</header>
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<p>For an introduction to the prompt buffer features and background story, see <a href="./prompt-buffer.org">our other article</a>.</p>
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<p><img src="../static/image/article/prompt-buffer-set-url.png" /></p>
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<p>In this article, we will review the API of the prompt buffer and see how the user can leverage this to write a custom prompt buffer.</p>
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<h1 id="api-and-customization">API and customization</h1>
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<h2 id="invocation">Invocation</h2>
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<p>A prompt buffer is invoked with the <code>prompt</code> command. For instance, in <code>set-url</code> we can find:</p>
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<div class="sourceCode" id="cb1" data-org-language="lisp"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb1-1" data-line-number="1">(prompt</a>
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<a class="sourceLine" id="cb1-2" data-line-number="2"> :prompt <span class="st">"Open URL"</span></a>
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<a class="sourceLine" id="cb1-3" data-line-number="3"> <span class="bu">:input</span> (<span class="kw">if</span> prefill-current-url-p</a>
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<a class="sourceLine" id="cb1-4" data-line-number="4"> (render-url (url (current-buffer))) <span class="st">""</span>)</a>
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<a class="sourceLine" id="cb1-5" data-line-number="5"> :history history</a>
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<a class="sourceLine" id="cb1-6" data-line-number="6"> <span class="co">;; `actions' are defined elsewhere, more details below.</span></a>
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<a class="sourceLine" id="cb1-7" data-line-number="7"> :sources (<span class="kw">list</span> (<span class="kw">make-instance</span> 'new-url-or-search-source :actions actions)</a>
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<a class="sourceLine" id="cb1-8" data-line-number="8"> (<span class="kw">make-instance</span> 'global-history-source :actions actions)</a>
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<a class="sourceLine" id="cb1-9" data-line-number="9"> (<span class="kw">make-instance</span> 'bookmark-source :actions actions)</a>
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<a class="sourceLine" id="cb1-10" data-line-number="10"> (<span class="kw">make-instance</span> 'search-engine-url-source :actions actions)))</a></code></pre></div>
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<p>The only required parameters are <code>:prompt</code> and the <code>:sources</code>.</p>
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<h2 id="sources">Sources</h2>
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<p>Much of the prompt configuration actually happens in the sources themselves.</p>
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<p>A source is just a class that inherits from <code>prompter:source</code>. For instance the aforementioned <code>global-history-source</code> could be defined with</p>
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<div class="sourceCode" id="cb2" data-org-language="lisp"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb2-1" data-line-number="1">(define-class global-history-source (prompter:source)</a>
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<a class="sourceLine" id="cb2-2" data-line-number="2"> ((prompter:name <span class="st">"Global history"</span>)</a>
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<a class="sourceLine" id="cb2-3" data-line-number="3"> (prompter:constructor (<span class="kw">lambda</span> (source)</a>
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<a class="sourceLine" id="cb2-4" data-line-number="4"> (<span class="kw">declare</span> (<span class="kw">ignorable</span> source))</a>
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<a class="sourceLine" id="cb2-5" data-line-number="5"> (history-initial-suggestions)))</a>
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<a class="sourceLine" id="cb2-6" data-line-number="6"> (prompter:filter-preprocessor <span class="kw">nil</span>) <span class="co">; Don't remove non-exact results.</span></a>
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<a class="sourceLine" id="cb2-7" data-line-number="7"> (prompter:actions '(buffer-load)))</a>
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<a class="sourceLine" id="cb2-8" data-line-number="8"> (:export-class-name-p <span class="kw">t</span>))</a></code></pre></div>
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<p>The required slots are <code>prompter:name</code> and <code>prompter:constructor</code>. The latter provides a list of initial suggestions. If a list, the suggestions are immediately available. If a function, the initial suggestions are computed asynchronously, which is useful to avoid delaying the prompt display in case the initial suggestions take time to compute.</p>
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<h2 id="actions">Actions</h2>
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<p>Actions are provided as a list of commands via the <code>prompter:actions</code> slot. The above source has one action by default. It's possible to locally extend sources when invoking a prompt. For instance, in <code>set-url</code> we have</p>
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<div class="sourceCode" id="cb3" data-org-language="lisp"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb3-1" data-line-number="1">(<span class="kw">let</span> (<span class="co">;; ...</span></a>
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<a class="sourceLine" id="cb3-2" data-line-number="2"> (actions (<span class="kw">list</span> (make-unmapped-command buffer-load)</a>
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<a class="sourceLine" id="cb3-3" data-line-number="3"> (make-command new-buffer-load (suggestion-values)</a>
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<a class="sourceLine" id="cb3-4" data-line-number="4"> <span class="st">"Load a URL in a new buffer."</span></a>
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<a class="sourceLine" id="cb3-5" data-line-number="5"> (make-buffer-focus :url (url (<span class="kw">first</span> suggestion-values)))))))</a>
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<a class="sourceLine" id="cb3-6" data-line-number="6"> <span class="co">;; ...</span></a>
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<a class="sourceLine" id="cb3-7" data-line-number="7"> )</a></code></pre></div>
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<p>Then <code>actions</code> is passed to the various source instantiations as in:</p>
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<div class="sourceCode" id="cb4" data-org-language="lisp"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb4-1" data-line-number="1">(<span class="kw">make-instance</span> 'global-history-source :actions actions)</a></code></pre></div>
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<p>An action is either a well-named command, as with buffer-load, or a locally-defined command like in the previous snippet.</p>
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<p>Some more details are needed here:</p>
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<ul>
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<li><p><code>make-command</code> is like <code>define-command</code> and returns a <code>command</code> object without defining it globally.</p>
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<p>Thus <code>new-buffer-load</code> above won't be listed in <code>execute-command</code>.</p></li>
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<li><p><code>make-unmapped-command</code> transform a function into another one that takes a list as argument and runs the original function over the first element only.</p>
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<p>Since prompts always return a list of suggestions (even when there is only one selected suggestion), this macro comes in handy to run existing functions over lists of 1 element.</p></li>
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</ul>
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<h2 id="attributes">Attributes</h2>
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<p>Suggestion values are arbitrary objects: strings, numbers, URLs, structures… For compound structures, it's interesting to display the various parts of the objects (for instance, display the slots of a class).</p>
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<p>This is where the <code>prompter:object-attributes</code> method comes into play. The <code>global-history-source</code> above lists suggestions of the <code>history-entry</code> type. To display something more meaninful than a bunch of</p>
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<div class="sourceCode" id="cb5" data-org-language="lisp"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb5-1" data-line-number="1">#<HISTORY-ENTRY {100924F7F3}<span class="op">></span></a></code></pre></div>
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<p>in the prompt buffer, we can specialize the aforementioned method:</p>
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<div class="sourceCode" id="cb6" data-org-language="lisp"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb6-1" data-line-number="1">(<span class="kw">defmethod</span><span class="fu"> prompter</span>:object-attributes ((entry history-entry))</a>
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<a class="sourceLine" id="cb6-2" data-line-number="2"> `((<span class="st">"URL"</span> ,(render-url (url entry)))</a>
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<a class="sourceLine" id="cb6-3" data-line-number="3"> (<span class="st">"Title"</span> ,(title entry))))</a></code></pre></div>
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<p>Now the suggestions are printed as</p>
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<pre><code>https://example.org Example Domain
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https://nyxt.atlas.engineer Nyxt
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...
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</code></pre>
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<p>and all columns are automatically aligned for you!</p>
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<h2 id="filters-suggestion-processing">Filters (suggestion processing)</h2>
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<p>Whenever the user inputs a character in the prompt buffer, the suggestions of all sources are processed.</p>
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<ul>
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<li><p>The <code>prompter:filter-preprocessor</code> is called on the whole list of suggestions. In particular, this means that the preprocessor can remove duplicates.</p>
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<p>The source won't display anything until the filter-preprocessor is done.</p></li>
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<li><p>Then, the <code>prompter:filter</code> is run over the suggestions returned by the preprocessor, one after the other.</p>
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<p>This per-suggestion stepping allows the source view to update its display at regular intervals until all suggestions are filtered.</p>
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<p>This filter function is particularly useful to score suggestions by relevance.</p></li>
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<li><p>Finally, the <code>prompter:filter-postprocessor</code> is run of the result of the filter, this time again over the entire list at once.</p>
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<p>Once again, the source view is only updated when the postprocessor is done with the whole list.</p></li>
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</ul>
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<p>The prompter is said to be <em>ready</em> when all its sources are <em>ready</em>, that is, when the preprocessor, the filter and the postprocessor have terminated for a given user input.</p>
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<h2 id="suggestion-objects">Suggestion objects</h2>
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<p>Internally, when the prompter filters and sorts suggestions, it wraps the list of initial values (arbitrary objects) into <code>suggestion</code> objects.</p>
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<p>It could be defined as follows:</p>
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<div class="sourceCode" id="cb8" data-org-language="lisp"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb8-1" data-line-number="1">(define-class suggestion ()</a>
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<a class="sourceLine" id="cb8-2" data-line-number="2"> ((value <span class="kw">nil</span></a>
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<a class="sourceLine" id="cb8-3" data-line-number="3"> <span class="bu">:type</span> <span class="kw">t</span>)</a>
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<a class="sourceLine" id="cb8-4" data-line-number="4"> (attributes '()</a>
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<a class="sourceLine" id="cb8-5" data-line-number="5"> :documentation <span class="st">"A non-dotted alist of attributes to structure the filtering.</span></a>
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<a class="sourceLine" id="cb8-6" data-line-number="6"><span class="st">Both the key and the value are strings."</span>)</a>
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<a class="sourceLine" id="cb8-7" data-line-number="7"> (match-data <span class="kw">nil</span></a>
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<a class="sourceLine" id="cb8-8" data-line-number="8"> <span class="bu">:type</span> <span class="kw">t</span></a>
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<a class="sourceLine" id="cb8-9" data-line-number="9"> :documentation <span class="st">"Arbitrary data that can be used by the `filter'</span></a>
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<a class="sourceLine" id="cb8-10" data-line-number="10"><span class="st">function and its preprocessors. It's the responsibility of the filter to ensure</span></a>
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<a class="sourceLine" id="cb8-11" data-line-number="11"><span class="st">the match-data is ready for its own use."</span>)</a>
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<a class="sourceLine" id="cb8-12" data-line-number="12"> (score <span class="fl">0.0</span></a>
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<a class="sourceLine" id="cb8-13" data-line-number="13"> :documentation <span class="st">"A score the can be set by the `filter' function and</span></a>
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<a class="sourceLine" id="cb8-14" data-line-number="14"><span class="st">used by the `sort-predicate'."</span>))</a>
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<a class="sourceLine" id="cb8-15" data-line-number="15"> (:documentation <span class="st">"Suggestions are processed and listed in `source'.</span></a>
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<a class="sourceLine" id="cb8-16" data-line-number="16"><span class="st">It wraps arbitrary object stored in the `value' slot.</span></a>
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<a class="sourceLine" id="cb8-17" data-line-number="17"><span class="st">The other slots are optional.</span></a>
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<a class="sourceLine" id="cb8-18" data-line-number="18"></a>
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<a class="sourceLine" id="cb8-19" data-line-number="19"><span class="st">Suggestions are made with the `suggestion-maker' slot from `source'."</span>))</a></code></pre></div>
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<p>This is useful to store information through the processing pipeline described in the previous section. For instance, the filter can calculate and store the score of each suggestion, in the <code>score</code> slot, which in turn is readily available to the <code>filter-postprocessor</code> for sorting and whatnot.</p>
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<h1 id="conclusion">Conclusion</h1>
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<p>We hope this inspires you to write awesome configurations and, why not, <a href="./the-thin-line-between-users-and-collaborators.org">extensions for Nyxt</a>!</p>
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<p>Thanks for reading :-)</p>
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