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POHow do keywords work in Common Lisp?
 

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  1. POHow do keywords work in Common Lisp?
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    <p>The question is not about <em>using</em> keywords, but actually about keyword <em>implementation</em>. For example, when I create some function with keyword parameters and make a call:</p> <pre><code>(defun fun (&amp;key key-param) (print key-param)) =&gt; FUN (find-symbol "KEY-PARAM" 'keyword) =&gt; NIL, NIL ;;keyword is not still registered (fun :key-param 1) =&gt; 1 (find-symbol "KEY-PARAM" 'keyword) =&gt; :KEY-PARAM, :EXTERNAL </code></pre> <p>How a keyword is used to pass an argument? Keywords are symbols whos values are themselves, so how a corresponding parameter can be bound using a keyword?</p> <p>Another question about keywords — keywords are used to define packages. We can define a package named with already existing keyword:</p> <pre><code>(defpackage :KEY-PARAM) =&gt; #&lt;The KEY-PARAMETER package, 0/16 ... (in-package :KEY-PARAM) =&gt; #&lt;The KEY-PARAMETER package, 0/16 ... (defun fun (&amp;key key-param) (print key-param)) =&gt; FUN (fun :KEY-PARAM 1) =&gt; 1 </code></pre> <p>How does system distinguish the usage of <code>:KEY-PARAM</code> between package name and function parameter name? Also we can make something more complicated, if we define function <code>KEY-PARAM</code> and export it (actually not function, but name):</p> <pre><code>(in-package :KEY-PARAM) (defun KEY-PARAM (&amp;key KEY-PARAM) KEY-PARAM) =&gt; KEY-PARAM (defpackage :KEY-PARAM (:export :KEY-PARAM)) ;;exporting function KEY-PARAM, :KEY-PARAM keyword is used for it (in-package :CL-USER) =&gt; #&lt;The COMMON-LISP-USER package, ... (KEY-PARAM:KEY-PARAM :KEY-PARAM 1) =&gt; 1 ;;calling a function KEY-PARAM from :KEY-PARAM package with :KEY-PARAM parameter... </code></pre> <p>The question is the same, how Common Lisp does distinguish the usage of keyword <code>:KEY-PARAM</code> here?</p> <p>If there is some manual about keywords in Common Lisp with explanation of their mechanics, I would be grateful if you posted a link here, because I could find just some short articles only about usage of the keywords.</p>
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