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make all of website use luan
author Franklin Schmidt <fschmidt@gmail.com>
date Thu, 23 Apr 2015 18:09:12 -0600
parents website/src/diff.html@f08cefa4594c
children 23d075ce1e48
comparison
equal deleted inserted replaced
385:9850d788a20b 386:db23f654f87d
1 local Io = require "luan:Io"
2 local Html = require "luan:Html"
3 local Http = require "luan:web/Http"
4
5
6 function service()
7 Io.stdout = Http.response.text_writer()
8 Html.simply_html_page{
9 head = function() %>
10 <title>How Luan differs from Lua</title>
11 <% end;
12 body = function() %>
13
14 <div container>
15 <div><small><a href="/">Luan</a></small></div>
16 <h1>How Luan differs from Lua</h1>
17
18 <p>This document explains how Luan differs from <a href="http://www.lua.org">Lua</a> as described in the <a href="http://www.lua.org/manual/5.3/">Lua 5.3 Reference Manual</a>.</p>
19
20 <hr/>
21
22 <h2>Contents</h2>
23
24 <div margin-bottom="1em"><a href="#intro">Introduction</a></div>
25
26 <div margin-bottom="1em">
27 <a href="#basic">Basic Concepts</a>
28 <ul>
29 <li><a href="#types">Values and Types</a></li>
30 <li><a href="#env">Environments</a></li>
31 <li><a href="#error">Error Handling</a></li>
32 <li><a href="#meta">Metatables and Metamethods</a></li>
33 <li><a href="#gc">Garbage Collection</a></li>
34 <li><a href="#coroutines">Coroutines</a></li>
35 </ul>
36 </div>
37
38 <div margin-bottom="1em">
39 <a href="#lang">The Language</a>
40 <ul>
41 <li><a href="#lex">Lexical Conventions</a></li>
42 <li>
43 <a href="#stmt">Statements</a>
44 <ul>
45 <li><a href="#control">Control Structures</a></li>
46 <li><a href="#for">For Statement</a></li>
47 <li><a href="#logical">Logical Statements</a></li>
48 <li><a href="#template-stmt">Template Statements</a></li>
49 </ul>
50 </li>
51 <li>
52 <a href="#expr">Expressions</a>
53 <ul>
54 <li><a href="#bit">Bitwise Operators</a></li>
55 <li><a href="#local-ops">Logical Operators</a></li>
56 <li><a href="#fn-call">Function Calls</a></li>
57 <li><a href="#template-expr">Template Expressions</a></li>
58 </ul>
59 </li>
60 </ul>
61 </div>
62
63 <hr/>
64
65 <h2 margin-top="1em"><a name="intro">Introduction</a></h2>
66
67 <p>Lua is one of the simplest languages available, but Luan is even simpler. This means Luan removes more than it adds. Most of what is added is added in the library, not in the language itself.</p>
68
69 <p>Luan is implemented in Java and is tightly integrated with Java. This makes it an excellent scripting language for Java.</p>
70
71 <h2 margin-top="1em"><a name="basic">Basic Concepts</a></h2>
72
73 <h3 margin-top="1em"><a name="types">Values and Types</a></h3>
74
75 <p>Luan does not have the Lua <i>thread</i> type. Luan add a <i>binary</i> type that Lua doesn't have. This is because Lua strings can represent binary while Luan strings cannot.</p>
76
77 <p>The Luan <i>Nil</i> type is implemented as the Java <i>null</i>. The Luan <i>Boolean</i> type is implemented as the Java <i>Boolean</i> type. The Luan <i>Number</i> type is implemented as the Java <i>Number</i> type. The Luan <i>String</i> type is implemented as the Java <i>String</i> type. Actual numbers may be any subclass of the Java <i>Number</i> class.</p>
78
79 <p>Luan functions may be written in Luan or may be wrappers around native Java methods. Any Java method may be called as a Luan function.</p>
80
81 <p>Luan <i>userdata</i> is nothing more than a Java object that doesn't fall into one of the other recognized types.</p>
82
83 <p>The Luan <i>binary</i> type is the Java <i>byte[ ]</i> type which is an array of bytes.</p>
84
85 <p>The Luan <i>table</i> type is just like its Lua equivalent, but implemented in Java.</p>
86
87 <h3 margin-top="1em"><a name="env">Environments</a></h3>
88
89 <p>Luan has an <tt>_ENV</tt> which is like its Lua equivalent. However Luan has no global environment at all, no <tt>_G</tt>.</p>
90
91 <p>Every module is initialized with two local functions: <tt>require</tt> and <tt>java</tt>. The module then uses these functions to get access to whatever else it needs.</p>
92
93 <h3 margin-top="1em"><a name="error">Error Handling</a></h3>
94
95 <p>Luan has the functions <tt>error</tt> and <tt>pcall</tt> but does not have <tt>xpcall</tt>. Luan adds the function <tt>try</tt> which looks and acts like try-catch blocks in other languages.</p>
96
97 <h3 margin-top="1em"><a name="meta">Metatables and Metamethods</a></h3>
98
99 <p>to document later...</p>
100
101 <h3 margin-top="1em"><a name="gc">Garbage Collection</a></h3>
102
103 <p>Luan uses Java garbage collection. Luan has no special garbage collection methods.</p>
104
105 <p>Luan does not yet have weak tables but this will be added.</p>
106
107 <h3 margin-top="1em"><a name="coroutines">Coroutines</a></h3>
108
109 <p>Luan does not have coroutines. Coroutines is a complex concept that isn't needed in a simple language, so it was left out.</p>
110
111 <h2 margin-top="1em"><a name="lang">The Language</a></h2>
112
113 <h3 margin-top="1em"><a name="lex">Lexical Conventions</a></h3>
114
115 <p>Unlike Lua, Luan generally considers the end of a line to be the end of a statement. This catches errors and encourages readability. The exception to this is in paranthesis ( <i>(...)</i>, <i>[...]</i>, and <i>{...}</i> ) where the end of line is treated as white space.</p>
116
117 <p>Luan has exactly the same set of keywords as Lua and has the same other lexical conventions.</p>
118
119 <h3 margin-top="1em"><a name="stmt">Statements</a></h3>
120
121 <p>Most statements in Luan are the same as Lua. Only those statements that differ will be listed here.</p>
122
123 <h4 margin-top="1em"><a name="control">Control Structures</a></h4>
124
125 <p>The Luan <b>if</b>, <b>while</b>, and <b>repeat</b> statement are the same as in Lua except that the condition expression must return a boolean value. Any other value type will produce an error. This helps catch errors and makes code more readable.</p>
126
127 <p>Luan does not have a <b>goto</b> statement.</p>
128
129 <h4 margin-top="1em"><a name="for">For Statement</a></h4>
130
131 <p>Luan has no numeric <b>for</b> statement. Luan only has generic <b>for</b> statement. Instead of the numeric <b>for</b> statement, Luan uses the <tt>range</tt> function in a generic <b>for</b> statement like this:</p>
132
133 <tt><pre>
134 for i in range(from,to,step) do <i>block</i> end
135 </pre></tt>
136
137 <p>The Luan generic <b>for</b> statement is simpler than the Lua version because Luan only uses and expression, not an explist. So a <b>for</b> statement like:</p>
138
139 <tt><pre>
140 for var_1, ···, var_n in exp do block end
141 </pre></tt>
142
143 <p>is equivalent to the code:</p>
144
145 <tt><pre>
146 do
147 local f = exp
148 while true do
149 local var_1, ···, var_n = f()
150 if var_1 == nil then break end
151 block
152 end
153 end
154 </pre></tt>
155
156 <h4 margin-top="1em"><a name="logical">Logical Statements</a></h4>
157
158 <p>Unlike Lua, Luan allows <b>or</b> and <b>and</b> expressions to be stand-alone statements. This is useful in cases like this:</p>
159
160 <tt><pre>
161 x==5 or error "x should be 5"
162 </pre></tt>
163
164 <h4 margin-top="1em"><a name="template-stmt">Template Statements</a></h4>
165
166 <p>Template statements are based on <a href="#template-expr">template exressions</a> and provide the full equivalent of <a href="http://en.wikipedia.org/wiki/JavaServer_Pages">JSP</a> but in a general way. Template statements write the equivalent template exression to standard output. For example:</p>
167
168 <tt><pre><%=Html.encode[[
169 local name = "Bob"
170 %>
171 Hello <%=name%>!
172 Bye <%=name%>.
173 <%
174 ]]%></pre></tt>
175
176 <p>is equivalent to the code:</p>
177
178 <tt><pre><%=Html.encode[[
179 local name = "Bob"
180 require("luan:Io").stdout.write( %>
181 Hello <%=name%>!
182 Bye <%=name%>.
183 <% )
184 ]]%></pre></tt>
185
186 <h3 margin-top="1em"><a name="expr">Expressions</a></h3>
187
188 <h4 margin-top="1em"><a name="bit">Bitwise Operators</a></h4>
189
190 <p>Bitwise operators appear to be new addition to Lua 5.3 and didn't exist in Lua 5.2. Luan does not support bitwise operators, but these can be added if there is a need.</p>
191
192 <h4 margin-top="1em"><a name="local-ops">Logical Operators</a></h4>
193
194 <p>The only change in Luan is that <b>not</b> must take a boolean argument. This helps catch errors and makes code more readable.</p>
195
196 <h4 margin-top="1em"><a name="fn-call">Function Calls</a></h4>
197
198 <p>Luan does not support Lua's <tt>v:name(args)</tt> style object-oriented function call. Object oriented programming is done in Luan using closures, so this feature is not needed.</p>
199
200 <h4 margin-top="1em"><a name="template-expr">Template Expressions</a></h4>
201
202 <p>Luan adds a new type of expression based on <a href="http://en.wikipedia.org/wiki/JavaServer_Pages">JSP</a> called template expressions. Template expressions return multiple values. Here is an example:</p>
203
204 <tt><pre><%=Html.encode[[
205 local name = "Bob"
206 write( %>Hello <%=name%>!<% )
207 ]]%></pre></tt>
208
209 <p>This is equivalent to the code:</p>
210
211 <tt><pre>
212 local name = "Bob"
213 write( "Hello ", name, "!" )
214 </pre></tt>
215
216 <p>The strings in template expressions may be multiple lines.</p>
217
218 </div>
219
220 <% end;
221 }
222 end