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<!-- 2024-04-21 ned 17:35 -->
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<!-- 2024-05-21 Tue 01:52 -->
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<title>Zapiski #1 srečanja programerskega bralnega krožka SICP</title>
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</script>
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</head>
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<body>
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<div id="content" class="content">
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<h1 class="title">Zapiski #1 srečanja programerskega bralnega krožka SICP</h1>
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<div id="outline-container-org42dee3b" class="outline-2">
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<h2 id="org42dee3b">Zanimivi izseki</h2>
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<div class="outline-text-2" id="text-org42dee3b">
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<div id="outline-container-org7918841" class="outline-2">
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<h2 id="org7918841">Zanimivi izseki</h2>
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<div class="outline-text-2" id="text-org7918841">
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</div>
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<div id="outline-container-orgdf32ea0" class="outline-3">
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<h3 id="orgdf32ea0">str. 9</h3>
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<div class="outline-text-3" id="text-orgdf32ea0">
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<div id="outline-container-orge5ee826" class="outline-3">
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<h3 id="orge5ee826">str. 9</h3>
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<div class="outline-text-3" id="text-orge5ee826">
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<blockquote>
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<p>
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Every reader should ask himself periodically "Toward what end, toward what end?" — but do not ask it too often lest you pass up the fun of programming for the constipation of bittersweet philosophy.
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@ -218,9 +434,10 @@ Lisp is a survivor, having been in use for about a quarter of a century.
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</blockquote>
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</div>
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</div>
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<div id="outline-container-org8373b18" class="outline-3">
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<h3 id="org8373b18">str. 11</h3>
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<div class="outline-text-3" id="text-org8373b18">
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<div id="outline-container-orgfc4618a" class="outline-3">
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<h3 id="orgfc4618a">str. 11</h3>
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<div class="outline-text-3" id="text-orgfc4618a">
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<blockquote>
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<p>
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It is better to have 100 functions operate on one data structure than to have 10 functions operate on 10 data structures.
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@ -228,9 +445,10 @@ It is better to have 100 functions operate on one data structure than to have 10
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</blockquote>
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</div>
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</div>
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<div id="outline-container-org3dac309" class="outline-3">
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<h3 id="org3dac309">str. 18</h3>
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<div class="outline-text-3" id="text-org3dac309">
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<div id="outline-container-org63a72bc" class="outline-3">
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<h3 id="org63a72bc">str. 18</h3>
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<div class="outline-text-3" id="text-org63a72bc">
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<blockquote>
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<p>
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Thus, programs must be written for people to read, and only incidentally for machines to execute.
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@ -238,9 +456,10 @@ Thus, programs must be written for people to read, and only incidentally for mac
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</blockquote>
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</div>
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</div>
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<div id="outline-container-org7994660" class="outline-3">
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<h3 id="org7994660">str. 19</h3>
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<div class="outline-text-3" id="text-org7994660">
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<div id="outline-container-org049ac46" class="outline-3">
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<h3 id="org049ac46">str. 19</h3>
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<div class="outline-text-3" id="text-org049ac46">
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<blockquote>
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<p>
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Underlying our approach to this subject is our conviction that "computer science" is not a science and that its significance has little to do with computers.
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@ -248,9 +467,10 @@ Underlying our approach to this subject is our conviction that "computer science
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</blockquote>
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</div>
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</div>
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<div id="outline-container-org3d45fa2" class="outline-3">
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<h3 id="org3d45fa2">str. 27</h3>
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<div class="outline-text-3" id="text-org3d45fa2">
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<div id="outline-container-org49a771f" class="outline-3">
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<h3 id="org49a771f">str. 27</h3>
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<div class="outline-text-3" id="text-org49a771f">
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<blockquote>
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<p>
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Finally, we would like to acknowledge the support of the organizations that have encouraged this work over the years, including support from Hewlett-Packard, made possible by Ira Goldstein and Joel Birnbaum, and support from DARPA, made possible by Bob Kahn.
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@ -271,31 +491,141 @@ Preko očeta v sorodu s fizikom Hermanom Kahnom, ki je napisal knjigo o tem kako
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</div>
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</div>
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<div id="outline-container-org0861788" class="outline-3">
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<h3 id="org0861788">str. 77</h3>
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<div class="outline-text-3" id="text-org0861788">
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<div id="outline-container-org6a8639c" class="outline-3">
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<h3 id="org6a8639c">str. 77</h3>
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<div class="outline-text-3" id="text-org6a8639c">
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<p>
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Stoy 1977
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</p>
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</div>
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</div>
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</div>
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<div id="outline-container-orgfcfaeb8" class="outline-2">
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<h2 id="orgfcfaeb8">Vaje</h2>
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<div class="outline-text-2" id="text-orgfcfaeb8">
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<div id="outline-container-org9007674" class="outline-2">
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<h2 id="org9007674">Vaje</h2>
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<div class="outline-text-2" id="text-org9007674">
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</div>
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<div id="outline-container-org9ddb5fa" class="outline-3">
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<h3 id="org9ddb5fa">1.1 Kaj vrnejo izrazi?</h3>
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<div id="outline-container-orgcf0051d" class="outline-3">
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<h3 id="orgcf0051d">1.1 Kaj vrnejo izrazi?</h3>
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<div class="outline-text-3" id="text-orgcf0051d">
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<div class="org-src-container">
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<pre class="src src-scheme"><span style="color: #458588;">(</span>+ 5 3 4<span style="color: #458588;">)</span>
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</pre>
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</div>
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<div id="outline-container-org77dfe73" class="outline-3">
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<h3 id="org77dfe73">1.2 Pretvori izraz v prefix obliko</h3>
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<div class="outline-text-3" id="text-org77dfe73">
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<p>
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10
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</p>
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<div class="org-src-container">
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<pre class="src src-scheme"><span style="color: #458588;">(</span>- 9 1<span style="color: #458588;">)</span>
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</pre>
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</div>
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<p>
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8
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</p>
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<div class="org-src-container">
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<pre class="src src-scheme"><span style="color: #458588;">(</span>/ 6 2<span style="color: #458588;">)</span>
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</pre>
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</div>
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<p>
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3
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</p>
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<div class="org-src-container">
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<pre class="src src-scheme"><span style="color: #458588;">(</span>+ <span style="color: #b16286;">(</span>* 2 4<span style="color: #b16286;">)</span> <span style="color: #b16286;">(</span>- 4 6<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
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</pre>
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</div>
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<p>
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6
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</p>
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<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #fabd2f;">a</span> 3<span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
#nil
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #fabd2f;">b</span> <span style="color: #b16286;">(</span>+ a 1<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
#nil
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span>+ a b <span style="color: #b16286;">(</span>* a b<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
19
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span>= a b<span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
#f
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">if</span> <span style="color: #b16286;">(</span><span style="color: #fb4933;">and</span> <span style="color: #8ec07c;">(</span>> b a<span style="color: #8ec07c;">)</span> <span style="color: #8ec07c;">(</span>< b <span style="color: #d65d0e;">(</span>* a b<span style="color: #d65d0e;">)</span><span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span>
|
||||
b
|
||||
a<span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
4
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">cond</span> <span style="color: #b16286;">(</span><span style="color: #8ec07c;">(</span>= a 4<span style="color: #8ec07c;">)</span> 6<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #8ec07c;">(</span>= b 4<span style="color: #8ec07c;">)</span> <span style="color: #8ec07c;">(</span>+ 6 7 a<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #fb4933;">else</span> 25<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
16
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span>+ 2 <span style="color: #b16286;">(</span><span style="color: #fb4933;">if</span> <span style="color: #8ec07c;">(</span>> b a<span style="color: #8ec07c;">)</span> b a<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
6
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span>* <span style="color: #b16286;">(</span><span style="color: #fb4933;">cond</span> <span style="color: #8ec07c;">(</span><span style="color: #d65d0e;">(</span>> a b<span style="color: #d65d0e;">)</span> a<span style="color: #8ec07c;">)</span>
|
||||
<span style="color: #8ec07c;">(</span><span style="color: #d65d0e;">(</span>< a b<span style="color: #d65d0e;">)</span> b<span style="color: #8ec07c;">)</span>
|
||||
<span style="color: #8ec07c;">(</span><span style="color: #fb4933;">else</span> -1<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>+ a 1<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
<p>
|
||||
16
|
||||
</p>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<div id="outline-container-orgd95ec59" class="outline-3">
|
||||
<h3 id="orgd95ec59">1.2 Pretvori izraz v prefix obliko</h3>
|
||||
<div class="outline-text-3" id="text-orgd95ec59">
|
||||
\begin{equation}
|
||||
\frac{5+4+(2-(3-(6+\frac{4}{5}))) }{3(6-2)(2-7)}
|
||||
\end{equation}
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span>/ <span style="color: #b16286;">(</span>+ 5 4
|
||||
<span style="color: #8ec07c;">(</span>- 2
|
||||
<span style="color: #d65d0e;">(</span>- 3
|
||||
<span style="color: #458588;">(</span>+ 6
|
||||
1/3<span style="color: #458588;">)</span><span style="color: #d65d0e;">)</span><span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span>
|
||||
4/5<span style="color: #458588;">)</span><span style="color: #d65d0e;">)</span><span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>* 3
|
||||
<span style="color: #8ec07c;">(</span>- 6 2<span style="color: #8ec07c;">)</span>
|
||||
<span style="color: #8ec07c;">(</span>- 2 7<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
|
@ -303,13 +633,14 @@ Stoy 1977
|
|||
</div>
|
||||
|
||||
<pre class="example">
|
||||
-43/180
|
||||
-37/150
|
||||
</pre>
|
||||
</div>
|
||||
</div>
|
||||
<div id="outline-container-org30e4913" class="outline-3">
|
||||
<h3 id="org30e4913">1.3 procedura, ki prejme 3 argumente in vrne vsoto kvadratov vecjih dveh</h3>
|
||||
<div class="outline-text-3" id="text-org30e4913">
|
||||
|
||||
<div id="outline-container-org40fcfc0" class="outline-3">
|
||||
<h3 id="org40fcfc0">1.3 določi postopek, ki prejme 3 števila kot argumente in vrne vsoto kvadratov večjih dveh</h3>
|
||||
<div class="outline-text-3" id="text-org40fcfc0">
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">vsota-vecjih-kvadratov</span> a b c<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #fb4933;">cond</span> <span style="color: #8ec07c;">(</span><span style="color: #d65d0e;">(</span><= a b c<span style="color: #d65d0e;">)</span> <span style="color: #d65d0e;">(</span>+ <span style="color: #458588;">(</span>* b b<span style="color: #458588;">)</span> <span style="color: #458588;">(</span>* c c<span style="color: #458588;">)</span><span style="color: #d65d0e;">)</span><span style="color: #8ec07c;">)</span>
|
||||
|
|
@ -328,7 +659,7 @@ Stoy 1977
|
|||
<span style="color: #d65d0e;">(</span>+kvadrat b c<span style="color: #d65d0e;">)</span><span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #458588;">(</span>list
|
||||
'<span style="color: #b16286;">(</span><span style="color: #b8bb26;">"Pricakovano"</span> 85 41 164 89<span style="color: #b16286;">)</span>
|
||||
'<span style="color: #b16286;">(</span><span style="color: #b8bb26;">"Pričakovano"</span> 85 41 164 89<span style="color: #b16286;">)</span>
|
||||
|
||||
<span style="color: #b16286;">(</span>list <span style="color: #b8bb26;">"Funkcija1"</span>
|
||||
<span style="color: #8ec07c;">(</span>vsota-vecjih-kvadratov 6 1 7<span style="color: #8ec07c;">)</span>
|
||||
|
|
@ -360,7 +691,7 @@ Stoy 1977
|
|||
</colgroup>
|
||||
<tbody>
|
||||
<tr>
|
||||
<td class="org-left">Pricakovano</td>
|
||||
<td class="org-left">Pričakovano</td>
|
||||
<td class="org-right">85</td>
|
||||
<td class="org-right">41</td>
|
||||
<td class="org-right">164</td>
|
||||
|
|
@ -387,14 +718,155 @@ Stoy 1977
|
|||
</div>
|
||||
</div>
|
||||
|
||||
<div id="outline-container-org9c2a7b0" class="outline-3">
|
||||
<h3 id="org9c2a7b0">1.4</h3>
|
||||
<div id="outline-container-orgc0b2345" class="outline-3">
|
||||
<h3 id="orgc0b2345">1.4 Opis procedure</h3>
|
||||
<div class="outline-text-3" id="text-orgc0b2345">
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">a-plus-abs-b</span> a b<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #8ec07c;">(</span><span style="color: #fb4933;">if</span> <span style="color: #d65d0e;">(</span>> b 0<span style="color: #d65d0e;">)</span> + -<span style="color: #8ec07c;">)</span> a b<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
|
||||
<p>
|
||||
Izraz <code>if</code> vrne funkcijo <code>+</code> ali <code>-</code> , glede na to, ali je argument <code>b</code> večji ali manjši od 0.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Če je <code>b</code> manjši od 0, ga odšteje od <code>a</code>, sicer pa ga prišeje. Zato je rezultat funkcije ekvivalenten vsoti <code>a</code> in absolutnega <code>b</code>.
|
||||
</p>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<div id="outline-container-orge0dc66d" class="outline-3">
|
||||
<h3 id="orge0dc66d">1.5 Aplikativni red in normalni red evalvacije</h3>
|
||||
<div class="outline-text-3" id="text-orge0dc66d">
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">p</span><span style="color: #b16286;">)</span> <span style="color: #b16286;">(</span>p<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">test</span> x y<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #fb4933;">if</span> <span style="color: #8ec07c;">(</span>= x 0<span style="color: #8ec07c;">)</span>
|
||||
0
|
||||
y<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #7c6f64;">;; </span><span style="color: #7c6f64;">Evalvira:</span>
|
||||
<span style="color: #458588;">(</span>test 0 <span style="color: #b16286;">(</span>p<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
|
||||
<p>
|
||||
Če interpreter deluje po aplikativnem zaporedju, bo najprej evalviral argumente. Ker je drugi argument postopek, ki v neskončnost vrača vrednost klica samega sebe, se bo program zaciklal oz. zmrznil.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Če pa interpreter deluje po normalnem zaporedju, bo pa začel izvajat postopek pred evalvacijo argumentov, le-te pa šele ko jih potrebuje. Tako bo, <code>if</code> stavek prepoznal ekvivalenco <code>x</code> in <code>0</code> ter vrnil <code>0</code>.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Klic takšne funkcije torej preveri ali interpreter deluje po aplikativnem ali normalnem zaporedju.
|
||||
</p>
|
||||
|
||||
<p>
|
||||
Guile scheme deluje po aplikativnem redu (in se zacikla). Normalni red pa lahko "simuliramo", če proceduro definiramo kot macro, z <code>define-case</code>. Klic macroja se ne zacikla.
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define-macro</span> <span style="color: #b16286;">(</span><span style="color: #83a598;">test-m</span> x y<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #fb4933;">if</span> <span style="color: #8ec07c;">(</span>= x 0<span style="color: #8ec07c;">)</span>
|
||||
0
|
||||
y<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #458588;">(</span>test-m 0 <span style="color: #b16286;">(</span>p<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
|
||||
<pre class="example">
|
||||
0
|
||||
</pre>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<div id="outline-container-orgba23aaa" class="outline-3">
|
||||
<h3 id="orgba23aaa">1.6 Novi if</h3>
|
||||
<div class="outline-text-3" id="text-orgba23aaa">
|
||||
<p>
|
||||
Imamo nov <code>if</code>, <code>new-if</code>.
|
||||
</p>
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">new-if</span> predicate then-clause else-clause<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #fb4933;">cond</span> <span style="color: #8ec07c;">(</span>predicate then-clause<span style="color: #8ec07c;">)</span>
|
||||
<span style="color: #8ec07c;">(</span><span style="color: #fb4933;">else</span> else-clause<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
|
||||
<p>
|
||||
Kaj se zgodi, če ga uporabimo za računanje kvadratnih korenov?
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">sqrt-iter</span> guess x<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>new-if <span style="color: #8ec07c;">(</span>good-enough? guess x<span style="color: #8ec07c;">)</span>
|
||||
guess
|
||||
<span style="color: #8ec07c;">(</span>sqrt-iter <span style="color: #d65d0e;">(</span>improve guess x<span style="color: #d65d0e;">)</span>
|
||||
x<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
|
||||
<p>
|
||||
Navaden <code>if</code> je v bistvu makro in deluje po normalnem zaporedju. Ker je <code>new-if</code> definiran kot procedura, mora zaradi aplikativnega zaporedja najprej evalvirati argumente. Zato se zacikla oz. zamrzne.
|
||||
</p>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<div id="outline-container-org7ed7ada" class="outline-3">
|
||||
<h3 id="org7ed7ada">1.7 good-enough? ni dovolj dober?</h3>
|
||||
<div class="outline-text-3" id="text-org7ed7ada">
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">average</span> x y<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>/ <span style="color: #8ec07c;">(</span>+ x y<span style="color: #8ec07c;">)</span> 2<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">improve</span> guess x<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>average guess <span style="color: #8ec07c;">(</span>/ x guess<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">good-enough?</span> guess x<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>< <span style="color: #8ec07c;">(</span>abs <span style="color: #d65d0e;">(</span>- <span style="color: #458588;">(</span>square guess<span style="color: #458588;">)</span> x<span style="color: #d65d0e;">)</span><span style="color: #8ec07c;">)</span> 0.001<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">sqrt-iter</span> guess x<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span><span style="color: #fb4933;">if</span> <span style="color: #8ec07c;">(</span>good-enough? guess x<span style="color: #8ec07c;">)</span>
|
||||
guess
|
||||
<span style="color: #8ec07c;">(</span>sqrt-iter <span style="color: #d65d0e;">(</span>improve guess x<span style="color: #d65d0e;">)</span>
|
||||
x<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
<span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">sqrt</span> x<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>sqrt-iter 1.0 x<span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
</pre>
|
||||
</div>
|
||||
|
||||
<p>
|
||||
Pri premajhnih številih <code>good-enough?</code> prehitro "odneha" in dobimo slab približek, pri prevelikih številih pa "predolgo vztraja", saj ne potrebujemo tako natančnega približka. Boljša rešitev s precej elegance je, recimo, primerjava s promilom <code>x</code> namesto 0.001.
|
||||
</p>
|
||||
|
||||
<div class="org-src-container">
|
||||
<pre class="src src-scheme"><span style="color: #458588;">(</span><span style="color: #fb4933;">define</span> <span style="color: #b16286;">(</span><span style="color: #fabd2f;">good-enough?</span> guess x<span style="color: #b16286;">)</span>
|
||||
<span style="color: #b16286;">(</span>< <span style="color: #8ec07c;">(</span>abs <span style="color: #d65d0e;">(</span>- <span style="color: #458588;">(</span>square guess<span style="color: #458588;">)</span> x<span style="color: #d65d0e;">)</span><span style="color: #8ec07c;">)</span> <span style="color: #8ec07c;">(</span>* 0.001 x<span style="color: #8ec07c;">)</span><span style="color: #b16286;">)</span><span style="color: #458588;">)</span>
|
||||
|
||||
</pre>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<div id="outline-container-org0c76570" class="outline-3">
|
||||
<h3 id="org0c76570">1.8 kubični koren</h3>
|
||||
<div class="outline-text-3" id="text-org0c76570">
|
||||
\begin{equation}
|
||||
\frac{x/y^{2}+2y}{3}
|
||||
\end{equation}
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div id="postamble" class="status">
|
||||
<p class="author">Author: Jurij</p>
|
||||
<p class="date">Created: 2024-04-21 ned 17:35</p>
|
||||
<p class="date">Created: 2024-05-21 Tue 01:52</p>
|
||||
<p class="validation"><a href="https://validator.w3.org/check?uri=referer">Validate</a></p>
|
||||
</div>
|
||||
</body>
|
||||
|
|
|
|||
|
|
@ -1,6 +1,6 @@
|
|||
#+TITLE: Zapiski #1 srečanja programerskega bralnega krožka SICP
|
||||
#+AUTHOR: Jurij
|
||||
#+OPTIONS: toc:nil num:nil author
|
||||
#+OPTIONS: toc:nil num:nil author tex:dvisvgm
|
||||
|
||||
* Zanimivi izseki
|
||||
** str. 9
|
||||
|
|
@ -11,18 +11,22 @@ Every reader should ask himself periodically "Toward what end, toward what end?"
|
|||
#+begin_quote
|
||||
Lisp is a survivor, having been in use for about a quarter of a century.
|
||||
#+end_quote
|
||||
|
||||
** str. 11
|
||||
#+begin_quote
|
||||
It is better to have 100 functions operate on one data structure than to have 10 functions operate on 10 data structures.
|
||||
#+end_quote
|
||||
|
||||
** str. 18
|
||||
#+begin_quote
|
||||
Thus, programs must be written for people to read, and only incidentally for machines to execute.
|
||||
#+end_quote
|
||||
|
||||
** str. 19
|
||||
#+begin_quote
|
||||
Underlying our approach to this subject is our conviction that "computer science" is not a science and that its significance has little to do with computers.
|
||||
#+end_quote
|
||||
|
||||
** str. 27
|
||||
#+begin_quote
|
||||
Finally, we would like to acknowledge the support of the organizations that have encouraged this work over the years, including support from Hewlett-Packard, made possible by Ira Goldstein and Joel Birnbaum, and support from DARPA, made possible by Bob Kahn.
|
||||
|
|
@ -36,29 +40,87 @@ Preko očeta v sorodu s fizikom Hermanom Kahnom, ki je napisal knjigo o tem kako
|
|||
|
||||
** str. 77
|
||||
Stoy 1977
|
||||
|
||||
* Vaje
|
||||
** 1.1 Kaj vrnejo izrazi?
|
||||
- 10
|
||||
- 12
|
||||
- 8
|
||||
- 3
|
||||
- 6
|
||||
- /
|
||||
- /
|
||||
- 19
|
||||
- #f
|
||||
- 4
|
||||
- 16
|
||||
- 6
|
||||
- 16
|
||||
#+begin_src scheme
|
||||
(+ 5 3 4)
|
||||
#+end_src
|
||||
10
|
||||
|
||||
#+begin_src scheme
|
||||
(- 9 1)
|
||||
#+end_src
|
||||
8
|
||||
|
||||
#+begin_src scheme
|
||||
(/ 6 2)
|
||||
#+end_src
|
||||
3
|
||||
|
||||
#+begin_src scheme
|
||||
(+ (* 2 4) (- 4 6))
|
||||
#+end_src
|
||||
6
|
||||
|
||||
#+begin_src scheme
|
||||
(define a 3)
|
||||
#+end_src
|
||||
#nil
|
||||
|
||||
#+begin_src scheme
|
||||
(define b (+ a 1))
|
||||
#+end_src
|
||||
#nil
|
||||
|
||||
#+begin_src scheme
|
||||
(+ a b (* a b))
|
||||
#+end_src
|
||||
19
|
||||
|
||||
#+begin_src scheme
|
||||
(= a b)
|
||||
#+end_src
|
||||
#f
|
||||
|
||||
#+begin_src scheme
|
||||
(if (and (> b a) (< b (* a b)))
|
||||
b
|
||||
a)
|
||||
#+end_src
|
||||
4
|
||||
|
||||
#+begin_src scheme
|
||||
(cond ((= a 4) 6)
|
||||
((= b 4) (+ 6 7 a))
|
||||
(else 25))
|
||||
#+end_src
|
||||
16
|
||||
|
||||
#+begin_src scheme
|
||||
(+ 2 (if (> b a) b a))
|
||||
#+end_src
|
||||
6
|
||||
|
||||
#+begin_src scheme
|
||||
(* (cond ((> a b) a)
|
||||
((< a b) b)
|
||||
(else -1))
|
||||
(+ a 1))
|
||||
#+end_src
|
||||
16
|
||||
|
||||
** 1.2 Pretvori izraz v prefix obliko
|
||||
\begin{equation}
|
||||
\frac{5+4+(2-(3-(6+\frac{4}{5}))) }{3(6-2)(2-7)}
|
||||
\end{equation}
|
||||
|
||||
#+begin_src scheme :exports both
|
||||
(/ (+ 5 4
|
||||
(- 2
|
||||
(- 3
|
||||
(+ 6
|
||||
1/3))))
|
||||
4/5))))
|
||||
(* 3
|
||||
(- 6 2)
|
||||
(- 2 7)))
|
||||
|
|
@ -66,7 +128,8 @@ Stoy 1977
|
|||
|
||||
#+RESULTS:
|
||||
: -43/180
|
||||
** 1.3 procedura, ki prejme 3 argumente in vrne vsoto kvadratov vecjih dveh
|
||||
|
||||
** 1.3 določi postopek, ki prejme 3 števila kot argumente in vrne vsoto kvadratov večjih dveh
|
||||
|
||||
#+begin_src scheme :exports both :results table
|
||||
(define (vsota-vecjih-kvadratov a b c)
|
||||
|
|
@ -86,7 +149,7 @@ Stoy 1977
|
|||
(+kvadrat b c))))
|
||||
|
||||
(list
|
||||
'("Pricakovano" 85 41 164 89)
|
||||
'("Pričakovano" 85 41 164 89)
|
||||
|
||||
(list "Funkcija1"
|
||||
(vsota-vecjih-kvadratov 6 1 7)
|
||||
|
|
@ -114,7 +177,7 @@ Stoy 1977
|
|||
|
||||
Izraz ~if~ vrne funkcijo ~+~ ali ~-~ , glede na to, ali je argument ~b~ večji ali manjši od 0.
|
||||
|
||||
Če je ~b~ manjši od 0, ga odšteje od ~a~, sicer pa ga prišeje. Zato je rezultat funkcije ekvivalenten vsoti ~a~ in absolutni vrednosti ~b~.
|
||||
Če je ~b~ manjši od 0, ga odšteje od ~a~, sicer pa ga prišeje. Zato je rezultat funkcije ekvivalenten vsoti ~a~ in absolutnega ~b~.
|
||||
|
||||
** 1.5 Aplikativni red in normalni red evalvacije
|
||||
|
||||
|
|
@ -130,13 +193,83 @@ Izraz ~if~ vrne funkcijo ~+~ ali ~-~ , glede na to, ali je argument ~b~ večji a
|
|||
(test 0 (p))
|
||||
#+end_src
|
||||
|
||||
TODO!
|
||||
Če interpreter deluje po aplikativnem zaporedju, bo najprej evalviral argumente. Ker je drugi argument postopek, ki v neskončnost vrača vrednost klica samega sebe, se bo program zaciklal oz. zmrznil.
|
||||
|
||||
** 1.6 TODO
|
||||
Če pa interpreter deluje po normalnem zaporedju, bo pa začel izvajat postopek pred evalvacijo argumentov, le-te pa šele ko jih potrebuje. Tako bo, ~if~ stavek prepoznal ekvivalenco ~x~ in ~0~ ter vrnil ~0~.
|
||||
|
||||
** 1.7 TODO
|
||||
Klic takšne funkcije torej preveri ali interpreter deluje po aplikativnem ali normalnem zaporedju.
|
||||
Guile scheme deluje po aplikativnem redu (in se zacikla). Normalni red pa lahko "simuliramo", če proceduro definiramo kot macro, z ~define-case~. Klic macroja se ne zacikla.
|
||||
|
||||
** 1.8 TODO
|
||||
#+begin_src scheme :exports both
|
||||
(define-macro (test-m x y)
|
||||
(if (= x 0)
|
||||
0
|
||||
y))
|
||||
|
||||
(test-m 0 (p))
|
||||
#+end_src
|
||||
|
||||
#+RESULTS:
|
||||
: 0
|
||||
|
||||
** 1.6 Novi if
|
||||
Imamo nov ~if~, ~new-if~.
|
||||
#+begin_src scheme
|
||||
(define (new-if predicate then-clause else-clause)
|
||||
(cond (predicate then-clause)
|
||||
(else else-clause)))
|
||||
#+end_src
|
||||
|
||||
Kaj se zgodi, če ga uporabimo za računanje kvadratnih korenov?
|
||||
|
||||
#+begin_src scheme
|
||||
(define (sqrt-iter guess x)
|
||||
(new-if (good-enough? guess x)
|
||||
guess
|
||||
(sqrt-iter (improve guess x)
|
||||
x)))
|
||||
#+end_src
|
||||
|
||||
Navaden ~if~ je v bistvu makro in deluje po normalnem zaporedju. Ker je ~new-if~ definiran kot procedura, mora zaradi aplikativnega zaporedja najprej evalvirati argumente. Zato se zacikla oz. zamrzne.
|
||||
|
||||
** 1.7 good-enough? ni dovolj dober?
|
||||
|
||||
#+begin_src scheme
|
||||
(define (average x y)
|
||||
(/ (+ x y) 2))
|
||||
|
||||
(define (improve guess x)
|
||||
(average guess (/ x guess)))
|
||||
|
||||
(define (good-enough? guess x)
|
||||
(< (abs (- (square guess) x)) 0.001))
|
||||
|
||||
(define (sqrt-iter guess x)
|
||||
(if (good-enough? guess x)
|
||||
guess
|
||||
(sqrt-iter (improve guess x)
|
||||
x)))
|
||||
|
||||
(define (sqrt x)
|
||||
(sqrt-iter 1.0 x))
|
||||
#+end_src
|
||||
|
||||
Pri premajhnih številih ~good-enough?~ prehitro "odneha" in dobimo slab približek, pri prevelikih številih pa "predolgo vztraja", saj ne potrebujemo tako natančnega približka. Boljša rešitev s precej elegance je, recimo, primerjava s promilom ~x~ namesto 0.001.
|
||||
|
||||
#+begin_src scheme
|
||||
(define (good-enough? guess x)
|
||||
(< (abs (- (square guess) x)) (* 0.001 x)))
|
||||
|
||||
#+end_src
|
||||
|
||||
** 1.8 kubični koren
|
||||
|
||||
Formula za izboljšanje približka ~y~ kubičnemu korenu ~x~ je
|
||||
\begin{equation}
|
||||
\frac{x/y^{2}+2y}{3}
|
||||
\end{equation}
|
||||
|
||||
Postopek: TODO
|
||||
|
||||
** 1.10 Ackermannov postopek
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue