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138 | | - <article> |
139 | | - <h1>2 Diving In</h1> |
140 | | - |
141 | | -<h2>2.2 Atoms and Strings</h2> |
142 | | - |
143 | | -<h3>2.2.1 Atoms</h3> |
144 | | - |
145 | | -<p>Atoms are a data type in Erlang that is used to represent non-numerical |
146 | | -constants. In LFE, the typographical limitations of Erlang don't apply, since |
147 | | -they're always quoted in LFE ;-)</p> |
148 | | - |
149 | | -<p>Atoms have a value: the same as their text:</p> |
150 | | - |
151 | | -<figure class="highlight"><pre><code class="language-cl" data-lang="cl"><span class="nb">></span> <span class="ss">'strag</span> |
152 | | -<span class="nv">strag</span> |
153 | | -<span class="nb">></span></code></pre></figure> |
154 | | - |
155 | | -<p>We saw this in the section on Boolean operators with the atoms of <code>true</code> |
156 | | -and <code>false</code>. Since there are no Boolean types in Erlang or LFE, the atoms |
157 | | -<code>true</code> and <code>false</code> are used instead.</p> |
158 | | - |
159 | | -<p>Here are some more examples of atoms:</p> |
160 | | - |
161 | | -<figure class="highlight"><pre><code class="language-cl" data-lang="cl"><span class="nb">></span> <span class="ss">'Vogon</span> |
162 | | -<span class="nv">Vogon</span> |
163 | | -<span class="nb">></span> <span class="ss">'_Gargle_Blaster</span> |
164 | | -<span class="nv">_Gargle_Blaster</span> |
165 | | -<span class="nb">></span> <span class="ss">'+</span> |
166 | | -<span class="nb">+</span> |
167 | | -<span class="nb">></span> <span class="ss">'*</span> |
168 | | -<span class="nb">*</span> |
169 | | -<span class="nb">></span> <span class="ss">'|and now with hyperspace bypasses|</span> |
170 | | -<span class="nv">|and now with hyperspace bypasses|</span> |
171 | | -<span class="nb">></span></code></pre></figure> |
172 | | - |
173 | | -<p>Though very simple, atoms have a huge impact on our everyday use of Erlang and |
174 | | -LFE, primarily in the area of pattern matching. Hold that thought, though; |
175 | | -we're not quite ready for it yet!</p> |
176 | | - |
177 | | -<p>Furthermore, atoms are stored differently in Erlang than strings. They take up |
178 | | -less space and are more efficient to compare than strings.</p> |
179 | | - |
180 | | -<h3>2.2.2 Strings</h3> |
181 | | - |
182 | | -<p>Now we come to the oddball of Erlang: the string. In truth, there is no such |
183 | | -thing. Strings in Erlang are just lists of integers:</p> |
184 | | - |
185 | | -<figure class="highlight"><pre><code class="language-cl" data-lang="cl"><span class="nb">></span> <span class="s">"Don't Panic."</span> |
186 | | -<span class="s">"Don't Panic."</span> |
187 | | -<span class="nb">></span> <span class="p">(</span><span class="nb">list</span> <span class="mi">68</span> <span class="mi">111</span> <span class="mi">110</span> <span class="mi">39</span> <span class="mi">116</span> <span class="mi">32</span> <span class="mi">80</span> <span class="mi">97</span> <span class="mi">110</span> <span class="mi">105</span> <span class="mi">99</span> <span class="mi">46</span><span class="p">)</span> |
188 | | -<span class="s">"Don't Panic."</span> |
189 | | -<span class="nb">></span></code></pre></figure> |
190 | | - |
191 | | -<p>Because Erlang (and thus LFE) strings consume 8 bytes per character on 32-bit |
192 | | -systems and 16 bytes on 64-bit systems, they are not very efficient. As such, |
193 | | -if you need to work with long strings in LFE, you probably want to use |
194 | | -<code>(binary ...)</code>, but that's in the next section :-)</p> |
195 | | - |
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