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e31c7a27 » Erik 2008-07-22 Exercise 2 done. Horray! 1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
2 <html>
3 <head>
4 <title>RDoc Documentation</title>
5 <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
6 </head>
7 <body>
8 <h2>File: Practical.Erlang.rdoc</h2>
9 <table>
10 <tr><td>Path:</td><td>Practical.Erlang.rdoc</td></tr>
11 <tr><td>Modified:</td><td>Tue Jul 22 16:11:39 -0700 2008</td></tr>
91cc8fcd » Erik 2008-07-23 Finished out Practical Erla... 12 </table>
e31c7a27 » Erik 2008-07-22 Exercise 2 done. Horray! 13
14 <h1>OSCON 2008, Tutorial 4: Practical Erlang</h1>
15 <p>
16 This tutorial is not about the history of Erlang, comparing Erlang to other
17 languages, or a comprehensive overview.
18 </p>
19 <p>
20 The goal is that we can read and write erlang, understand the concurrency
21 model and the error handling model.
22 </p>
23 <h2>Basic Erlang</h2>
24 <h3>Starting the system</h3>
25 <pre>
26 erl
27 </pre>
28 <p>
29 You get some *1&gt;* and *2&gt;* stuff. End everything with a .
30 </p>
31 <h3>Data Types</h3>
32 <h4>Integers</h4>
33 <ul>
34 <li>10
35
36 </li>
37 <li>-234
38
39 </li>
40 <li>16#16 = conversion from hex
41
42 </li>
43 <li>2#101010 = conversion from binary
44
45 </li>
46 <li>$A = ASCII value of A
47
48 </li>
49 </ul>
50 <p>
51 There&#8216;s also floats.
52 </p>
53 <h4>Atoms</h4>
54 <p>
55 Constant literals, always lowercase letter or in quotes.
56 </p>
57 <h4>Tuples</h4>
58 <p>
59 Fixed number of elements, any size, and contain any valid Erlang
60 expression.
61 </p>
62 <h4>Lists</h4>
63 <ul>
64 <li>Variable number of elements
65
66 </li>
67 <li>dynamic size
68
69 </li>
70 <li>strings are lists of characters
71
72 </li>
73 <li>lists are encapsulated by *[]*
74
75 </li>
76 <li>empty string is an empty list
77
78 </li>
79 </ul>
80 <h5>Concatenation</h5>
81 <pre>
82 [1,2,3] ++ [4,5,6]
83 </pre>
84 <h4>Complex Data Structures</h4>
85 <ul>
86 <li>Just a big list generally, containing tuples.
87
88 </li>
89 <li>Uses a garbage collector.
90
91 </li>
92 </ul>
93 <h3>Pattern Matching</h3>
94 <ul>
95 <li>Pattern = Expression
96
97 </li>
98 </ul>
99 <h4>Assignment</h4>
100 <pre>
101 {B,C,D} = {10,foo,bar}.
102 [H|T] = [1,2,3]
103 </pre>
104 <h4>Testing</h4>
105 <pre>
106 {A,A,B} = {abc,def,123}.
107 </pre>
108 <p>
109 Fails because A is being reassigned
110 </p>
111 <pre>
112 [A,B,C,D] = [1,2,3]
113 </pre>
114 <p>
115 Fails because the lists are not the same size
116 </p>
117 <pre>
118 [A,B|C] = [1,2,3,4,5,6,7]
119 </pre>
120 <p>
121 Suceeds, A=1, B=2, and C=the rest
122 </p>
123 <pre>
124 [H|T] = []
125 </pre>
126 <p>
127 Fails since at least 1 element is needed on the right
128 </p>
129 <h3>Variables</h3>
130 <pre>
131 {A,_, [B|_], {B}} = {abc,23,[22,x], {22}}
132 </pre>
133 <p>
134 Succeeds - A=abc, B=22
135 </p>
136 <h3>Functions</h3>
137 <ul>
138 <li>You have to define functions with the correct arity.
139
140 </li>
141 <li>Need to be exported to be used outside
142
143 </li>
144 </ul>
145 <h2>Sequential Erlang</h2>
146 <h3>Conditionals</h3>
147 <h4>Case</h4>
148 <pre>
149 case lists:member(foo,List) of
150 true -&gt; ok;
151 false -&gt; {error, unknown}
152 end
153 </pre>
154 <ul>
155 <li>No punctuation on last <b>case</b> clause.
156
157 </li>
158 <li>Can evaluate one or more expressions per clause, seperated by ;.
159
160 </li>
161 <li>There&#8216;s a dont-care clause that can protect you from a runtime error.
162
163 </li>
164 </ul>
165 <h4>If</h4>
166 <pre>
167 if
168 X&lt;1 -&gt; smaller;
169 X&gt;1 -&gt; greater;
170 X==1 -&gt; equal
171 end
172 </pre>
173 <ul>
174 <li>true guard allows a default case. It&#8216;s not mandatory.
175
176 </li>
177 </ul>
178 <h4>Guards</h4>
179 <p>
180 We can use guards in functions using <b>when</b>.
181 </p>
182 <pre>
183 factorial(N) when N &gt; 0 -&gt;
184 N * factorial(N-1);
185 factorial(0) -&gt; 1.
186 </pre>
187 <p>
188 Since everything is pattern matched sequentially, we get a performance
189 improvement by having the N&gt;0 case first.
190 </p>
191 <pre>
192 is_number
193 is_atom
194 length
195 X == Y % Simply compares values
196 X =:= Y % Also compares data types
197 </pre>
198 <p>
199 All guards have to succeed here:
200 </p>
201 <pre>
202 swap(String) when is_list(String),
203 length(String) &lt; 10 -&gt; ...
204 </pre>
205 <p>
206 Only one guard has to succeed here:
207 </p>
208 <pre>
209 swap(Tuple) when is_tuple(Tuple);
210 is_atom(Tuple) -&gt; ...
211 </pre>
212 <h3>Recursion</h3>
213 <h4>Traversing lists</h4>
214 <pre>
215 average(X) -&gt; sum(X)/len(X).
216
217 sum([H|T]) -&gt; H + sum(T);
218 sum([]) -&gt; 0.
219
220 len([H|T]) -&gt; 1 + len(T);
221 len([]) -&gt; 0.
222 </pre>
223 <h4>More Patterns</h4>
224 <pre>
225 even([H|T]) when H rem 2 == 0 -&gt;
226 [H|even(T)];
227 even([_|T]) -&gt;
228 even(T);
229 even([]) -&gt;
230 [].
231 </pre>
232 <p>
233 Finds even numbers by using the first when clause, passing odds to the
234 second one, which simply calls even on the tail.
235 </p>
236 <pre>
237 double([H|T]) -&gt; [2*H|double(T)];
238 double([]) -&gt; [].
239
240 member(H, [H|_]) -&gt; true;
241 member(H, [_|T]) -&gt; member(H, T);
242 member(_, []) -&gt; false.
243 </pre>
244 <p>
245 Checks the head of the list equality with the element to search for. Fail,
246 then go through the rest of the list save the head.
247 </p>
248 <h4>Accumulators</h4>
249 <pre>
250 average(X) -&gt; average(X,0,0).
251
252 average([H|T], Length, Sum) -&gt;
253 average(T, Length + 1, Sum + H);
254 </pre>
255 <p>
256 Not sure about this part, he switched slides:
257 </p>
258 <pre>
259 average([], Length, Sum) -&gt;
260 Sum/Length;
261 </pre>
262 <h3>Builtin Functions</h3>
263 <pre>
264 63&gt; date().
265 {2008,7,22}
266 64&gt; time().
267 {15,5,32}
268 65&gt; length([1,2,3]).
269 3
270 66&gt; size({4,5,6}).
271 3
272 67&gt; atom_to_list(asd).
273 &quot;asd&quot;
274 </pre>
275 <ul>
276 <li>BIFs can modify realtime properties of the system
277
278 </li>
279 </ul>
280 <h4>Meta Calls</h4>
281 <pre>
282 apply(Module, Function, Args)
283
91cc8fcd » Erik 2008-07-23 Finished out Practical Erla... 284 68&gt; apply(boolean, b_not, [false]).
285 true
286 69&gt; apply(boolean, b_not, [true]).
287 false
288 </pre>
e31c7a27 » Erik 2008-07-22 Exercise 2 done. Horray! 289 <ul>
290 <li>Dynamically evaluate functions.
291
292 </li>
293 <li>Function must be exported
294
295 </li>
296 <li>Arguments established at runtime
297
298 </li>
299 <li>Extremely powerful when implementing generic code
300
301 </li>
302 </ul>
303 <h2>Creating Processes</h2>
91cc8fcd » Erik 2008-07-23 Finished out Practical Erla... 304 <pre>
305 Pid2 = spawn(Mod, Func, Arg)
306 </pre>
307 <h2>Message Passing</h2>
308 <pre>
309 Pid ! Msg
310 </pre>
311 <ul>
312 <li>Bang construct (!)
313
314 </li>
315 <li>Msg is any valid Erlang type
316
317 </li>
318 <li>Goes to the process mailbox, stores the message sequentially
319
320 </li>
321 </ul>
322 <h3>Receive Clause</h3>
323 <pre>
324 receive
325 {reset, Board} -&gt; reset(Board);
326 {shut_down, Board} -&gt; {error, unknown_msg}
327 end
328 </pre>
329 <ul>
330 <li>There is a non-blocking form of receive using an <b>after</b> clause.
331
332 </li>
333 </ul>
334 <h2>Concurrent Programming</h2>
e31c7a27 » Erik 2008-07-22 Exercise 2 done. Horray! 335 <h2>Process Error Handling</h2>
336
337
338
339
340
341
342
343 <h2>Classes</h2>
344 </body>
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