-
Notifications
You must be signed in to change notification settings - Fork 0
/
symbols.html
120 lines (120 loc) · 8.06 KB
/
symbols.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="" xml:lang="">
<head>
<meta charset="utf-8" />
<meta name="generator" content="pandoc" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
<title>symbols</title>
<style type="text/css">
code{white-space: pre-wrap;}
span.smallcaps{font-variant: small-caps;}
span.underline{text-decoration: underline;}
div.column{display: inline-block; vertical-align: top; width: 50%;}
</style>
<style type="text/css">
a.sourceLine { display: inline-block; line-height: 1.25; }
a.sourceLine { pointer-events: none; color: inherit; text-decoration: inherit; }
a.sourceLine:empty { height: 1.2em; }
.sourceCode { overflow: visible; }
code.sourceCode { white-space: pre; position: relative; }
div.sourceCode { margin: 1em 0; }
pre.sourceCode { margin: 0; }
@media screen {
div.sourceCode { overflow: auto; }
}
@media print {
code.sourceCode { white-space: pre-wrap; }
a.sourceLine { text-indent: -1em; padding-left: 1em; }
}
pre.numberSource a.sourceLine
{ position: relative; left: -4em; }
pre.numberSource a.sourceLine::before
{ content: attr(title);
position: relative; left: -1em; text-align: right; vertical-align: baseline;
border: none; pointer-events: all; display: inline-block;
-webkit-touch-callout: none; -webkit-user-select: none;
-khtml-user-select: none; -moz-user-select: none;
-ms-user-select: none; user-select: none;
padding: 0 4px; width: 4em;
background-color: #2a211c;
color: #bdae9d;
}
pre.numberSource { margin-left: 3em; border-left: 1px solid #bdae9d; padding-left: 4px; }
div.sourceCode
{ color: #bdae9d; background-color: #2a211c; }
@media screen {
a.sourceLine::before { text-decoration: underline; }
}
code span.al { color: #ffff00; } /* Alert */
code span.an { color: #0066ff; font-weight: bold; font-style: italic; } /* Annotation */
code span.at { } /* Attribute */
code span.bn { color: #44aa43; } /* BaseN */
code span.bu { } /* BuiltIn */
code span.cf { color: #43a8ed; font-weight: bold; } /* ControlFlow */
code span.ch { color: #049b0a; } /* Char */
code span.cn { } /* Constant */
code span.co { color: #0066ff; font-weight: bold; font-style: italic; } /* Comment */
code span.do { color: #0066ff; font-style: italic; } /* Documentation */
code span.dt { text-decoration: underline; } /* DataType */
code span.dv { color: #44aa43; } /* DecVal */
code span.er { color: #ffff00; font-weight: bold; } /* Error */
code span.ex { } /* Extension */
code span.fl { color: #44aa43; } /* Float */
code span.fu { color: #ff9358; font-weight: bold; } /* Function */
code span.im { } /* Import */
code span.in { color: #0066ff; font-weight: bold; font-style: italic; } /* Information */
code span.kw { color: #43a8ed; font-weight: bold; } /* Keyword */
code span.op { } /* Operator */
code span.pp { font-weight: bold; } /* Preprocessor */
code span.sc { color: #049b0a; } /* SpecialChar */
code span.ss { color: #049b0a; } /* SpecialString */
code span.st { color: #049b0a; } /* String */
code span.va { } /* Variable */
code span.vs { color: #049b0a; } /* VerbatimString */
code span.wa { color: #ffff00; font-weight: bold; } /* Warning */
</style>
<link rel="stylesheet" href="tufte.css" />
<!--[if lt IE 9]>
<script src="//cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv-printshiv.min.js"></script>
<![endif]-->
</head>
<body>
<p>#Symbols</p>
<p>Common Lisp is a Lisp 2. The only difference between a Lisp 1 and Lisp 2 is that Lisp 2 languages have two separate namespaces for values and functions. In Common Lisp this is managed using symbols. We can demonstrate this as follows, in the REPL:</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb1-1" title="1">CL-USER> (<span class="kw">inspect</span> <span class="dv">42</span>)</a>
<a class="sourceLine" id="cb1-2" title="2"></a>
<a class="sourceLine" id="cb1-3" title="3">The object is an ATOM:</a>
<a class="sourceLine" id="cb1-4" title="4"> <span class="dv">42</span></a></code></pre></div>
<p><code>inspect</code> is a function which reports on the internal representation of the object that is passed to it. In the example above, the number <code>42</code> which is an <code>ATOM</code>.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb2-1" title="1">CL-USER> (<span class="kw">inspect</span> 'foo)</a>
<a class="sourceLine" id="cb2-2" title="2"></a>
<a class="sourceLine" id="cb2-3" title="3">The object is a SYMBOL.</a>
<a class="sourceLine" id="cb2-4" title="4"><span class="fl">0.</span> Name: <span class="st">"FOO"</span></a>
<a class="sourceLine" id="cb2-5" title="5"><span class="fl">1.</span> Package: #<PACKAGE <span class="st">"COMMON-LISP-USER"</span>></a>
<a class="sourceLine" id="cb2-6" title="6"><span class="fl">2.</span> Value: <span class="st">"unbound"</span></a>
<a class="sourceLine" id="cb2-7" title="7"><span class="fl">3.</span> Function: <span class="st">"unbound"</span></a>
<a class="sourceLine" id="cb2-8" title="8"><span class="fl">4.</span> Plist: NIL</a></code></pre></div>
<p>Here we <code>inspect</code> a symbol <code>foo</code> and we can see 5 “slots”. The <code>Name</code>, which is a unique identifier for the symbol. <code>Package</code>, which as you might expect defines a namespace in which the symbol exists. <code>Plist</code> is out of scope for this chapter, but we will look more deeply at <code>Value</code> and <code>Function</code>.</p>
<p>When we define a value “foo” we fill the <code>Value</code> slot on the symbol <code>foo</code>. For example:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb3-1" title="1"><span class="op">></span> (<span class="kw">defparameter</span><span class="fu"> foo </span><span class="st">"some value"</span>)</a>
<a class="sourceLine" id="cb3-2" title="2"></a>
<a class="sourceLine" id="cb3-3" title="3">FOO</a>
<a class="sourceLine" id="cb3-4" title="4"></a>
<a class="sourceLine" id="cb3-5" title="5">CL-USER> (<span class="kw">inspect</span> 'foo)</a>
<a class="sourceLine" id="cb3-6" title="6"></a>
<a class="sourceLine" id="cb3-7" title="7">The object is a SYMBOL.</a>
<a class="sourceLine" id="cb3-8" title="8"><span class="fl">0.</span> Name: <span class="st">"FOO"</span></a>
<a class="sourceLine" id="cb3-9" title="9"><span class="fl">1.</span> Package: #<PACKAGE <span class="st">"COMMON-LISP-USER"</span>></a>
<a class="sourceLine" id="cb3-10" title="10"><span class="fl">2.</span> Value: <span class="st">"some value"</span></a>
<a class="sourceLine" id="cb3-11" title="11"><span class="fl">3.</span> Function: <span class="st">"unbound"</span></a>
<a class="sourceLine" id="cb3-12" title="12"><span class="fl">4.</span> Plist: NIL</a></code></pre></div>
<p>The <code>Value</code> slot of <code>foo</code> now contains <code>"some value"</code>. Similarly, declaring a function <code>foo</code> will fill the <code>Function</code> slot on <code>foo</code></p>
<div class="sourceCode" id="cb4"><pre class="sourceCode commonlisp"><code class="sourceCode commonlisp"><a class="sourceLine" id="cb4-1" title="1">CL-USER> (<span class="kw">inspect</span> '(a b c))</a>
<a class="sourceLine" id="cb4-2" title="2"></a>
<a class="sourceLine" id="cb4-3" title="3">The object is a proper <span class="kw">list</span> of <span class="kw">length</span> <span class="fl">3.</span></a>
<a class="sourceLine" id="cb4-4" title="4"><span class="fl">0.</span> <span class="dv">0</span>: A</a>
<a class="sourceLine" id="cb4-5" title="5"><span class="fl">1.</span> <span class="dv">1</span>: B</a>
<a class="sourceLine" id="cb4-6" title="6"><span class="fl">2.</span> <span class="dv">2</span>: C</a></code></pre></div>
<p>In this example, a list is passed to <code>inspect</code>. We can see that the list has a numbered slot for each item, each item has an index and also a value.</p>
</body>
</html>