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website - improve docs
author Franklin Schmidt <fschmidt@gmail.com>
date Fri, 08 Feb 2019 00:45:31 -0700
parents 29d6d7d79c41
children f5368cd8c056
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1326:29d6d7d79c41 1327:b29eefad2111
11 <div small> 11 <div small>
12 <a href=".">Luan</a> 12 <a href=".">Luan</a>
13 / <a href="docs.html">Documentation</a> 13 / <a href="docs.html">Documentation</a>
14 </div> 14 </div>
15 15
16 <h1>How Luan differs from Lua</h1> 16 <h1><a href="diff.html">How Luan differs from Lua</a></h1>
17 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> 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 19
20 <hr/> 20 <hr/>
21 21
64 </ul> 64 </ul>
65 </div> 65 </div>
66 66
67 <hr/> 67 <hr/>
68 68
69 <h2 heading><a name="intro">Introduction</a></h2> 69 <h2 heading><a name="intro" href="#intro">Introduction</a></h2>
70 70
71 <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> 71 <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>
72 72
73 <p>Luan is implemented in Java and is tightly integrated with Java. This makes it an excellent scripting language for Java.</p> 73 <p>Luan is implemented in Java and is tightly integrated with Java. This makes it an excellent scripting language for Java.</p>
74 74
75 <h2 heading><a name="basic">Basic Concepts</a></h2> 75 <h2 heading><a name="basic" href="#basic">Basic Concepts</a></h2>
76 76
77 <h3 heading><a name="types">Values and Types</a></h3> 77 <h3 heading><a name="types" href="#types">Values and Types</a></h3>
78 78
79 <p>Luan does not have the Lua <em>thread</em> type. Luan adds a <em>binary</em> type that Lua doesn't have. This is because Lua strings can represent binary while Luan strings cannot.</p> 79 <p>Luan does not have the Lua <em>thread</em> type. Luan adds a <em>binary</em> type that Lua doesn't have. This is because Lua strings can represent binary while Luan strings cannot.</p>
80 80
81 <p>The Luan <em>Nil</em> type is implemented as the Java <em>null</em>. The Luan <em>Boolean</em> type is implemented as the Java <em>Boolean</em> type. The Luan <em>Number</em> type is implemented as the Java <em>Number</em> type. The Luan <em>String</em> type is implemented as the Java <em>String</em> type. Actual numbers may be any subclass of the Java <em>Number</em> class.</p> 81 <p>The Luan <em>Nil</em> type is implemented as the Java <em>null</em>. The Luan <em>Boolean</em> type is implemented as the Java <em>Boolean</em> type. The Luan <em>Number</em> type is implemented as the Java <em>Number</em> type. The Luan <em>String</em> type is implemented as the Java <em>String</em> type. Actual numbers may be any subclass of the Java <em>Number</em> class.</p>
82 82
86 86
87 <p>The Luan <em>binary</em> type is the Java <em>byte[ ]</em> type which is an array of bytes.</p> 87 <p>The Luan <em>binary</em> type is the Java <em>byte[ ]</em> type which is an array of bytes.</p>
88 88
89 <p>The Luan <em>table</em> type is just like its Lua equivalent, but implemented in Java.</p> 89 <p>The Luan <em>table</em> type is just like its Lua equivalent, but implemented in Java.</p>
90 90
91 <h3 heading><a name="env">Environments</a></h3> 91 <h3 heading><a name="env" href="#env">Environments</a></h3>
92 92
93 <p>Luan has no global environment at all, no <code>_G</code>. By default, Luan doesn't define <code>_ENV</code> either, but if you define it as a local table in a chunk, then it acts like it does in Lua. When <code>_ENV</code> isn't defined, there are no global variables and an unrecognized variable name produces a compile error.</p> 93 <p>Luan has no global environment at all, no <code>_G</code>. By default, Luan doesn't define <code>_ENV</code> either, but if you define it as a local table in a chunk, then it acts like it does in Lua. When <code>_ENV</code> isn't defined, there are no global variables and an unrecognized variable name produces a compile error.</p>
94 94
95 <p>Every module is initialized with two local functions: <code>require</code> and <code>java</code>. The module then uses these functions to get access to whatever else it needs.</p> 95 <p>Every module is initialized with two local functions: <code>require</code> and <code>java</code>. The module then uses these functions to get access to whatever else it needs.</p>
96 96
97 <h3 heading><a name="error">Error Handling</a></h3> 97 <h3 heading><a name="error" href="#error">Error Handling</a></h3>
98 98
99 <p>Luan has the functions <code>error</code> and <code>pcall</code> but does not have <code>xpcall</code>. Luan adds the function <code>try</code> which looks and acts like try-catch blocks in other languages. Luan errors are implemented as an error table, not as a message object.</p> 99 <p>Luan has the functions <code>error</code> and <code>pcall</code> but does not have <code>xpcall</code>. Luan adds the function <code>try</code> which looks and acts like try-catch blocks in other languages. Luan errors are implemented as an error table, not as a message object.</p>
100 100
101 <h3 heading><a name="meta">Metatables and Metamethods</a></h3> 101 <h3 heading><a name="meta" href="#meta">Metatables and Metamethods</a></h3>
102 102
103 <p>Luan only has metatable for tables, not for other types.</p> 103 <p>Luan only has metatable for tables, not for other types.</p>
104 104
105 <p>Luan does not support the <b>call</b> metamethod. There is nothing that one can do with the <b>call</b> metamethod that can't be done more cleanly with closures, so this was left out.</p> 105 <p>Luan does not support the <b>call</b> metamethod. There is nothing that one can do with the <b>call</b> metamethod that can't be done more cleanly with closures, so this was left out.</p>
106 106
107 <h3 heading><a name="gc">Garbage Collection</a></h3> 107 <h3 heading><a name="gc" href="#gc">Garbage Collection</a></h3>
108 108
109 <p>Luan uses Java garbage collection. Luan has no special garbage collection methods.</p> 109 <p>Luan uses Java garbage collection. Luan has no special garbage collection methods.</p>
110 110
111 <p>Luan does not yet have weak tables but this will be added.</p> 111 <p>Luan does not yet have weak tables but this will be added.</p>
112 112
113 <h3 heading><a name="coroutines">Coroutines</a></h3> 113 <h3 heading><a name="coroutines" href="#coroutines">Coroutines</a></h3>
114 114
115 <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> 115 <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>
116 116
117 <h2 heading><a name="lang">The Language</a></h2> 117 <h2 heading><a name="lang" href="#lang">The Language</a></h2>
118 118
119 <h3 heading><a name="lex">Lexical Conventions</a></h3> 119 <h3 heading><a name="lex" href="#lex">Lexical Conventions</a></h3>
120 120
121 <p>Unlike Lua, Luan considers the end of a line to be the end of a statement. This catches errors and encourages readability. If you want to continue a statement on another line, you can use a backslash followed by a newline which will be treated as white space.</p> 121 <p>Unlike Lua, Luan considers the end of a line to be the end of a statement. This catches errors and encourages readability. If you want to continue a statement on another line, you can use a backslash followed by a newline which will be treated as white space.</p>
122 122
123 <p>Luan has exactly the same set of keywords as Lua and has the same other lexical conventions.</p> 123 <p>Luan has exactly the same set of keywords as Lua and has the same other lexical conventions.</p>
124 124
125 <h3 heading><a name="vars">Variables</a></h3> 125 <h3 heading><a name="vars" href="#vars">Variables</a></h3>
126 126
127 <p> 127 <p>
128 By default, there are no global variables and an undefined variable produces a compile error. To enable global variables, one must define <code>_ENV</code>. Avoiding global variables makes it much easier to catch errors at compile time. 128 By default, there are no global variables and an undefined variable produces a compile error. To enable global variables, one must define <code>_ENV</code>. Avoiding global variables makes it much easier to catch errors at compile time.
129 129
130 <h3 heading><a name="stmt">Statements</a></h3> 130 <h3 heading><a name="stmt" href="#stmt">Statements</a></h3>
131 131
132 <p>Luan adds the block terminators <b>end_do</b>, <b>end_for</b>, <b>end_function</b>, <b>end_if</b>, and <b>end_while</b>. These can be used to end the appropriate block type, but <b>end</b> can also be used to end any block.</p> 132 <p>Luan adds the block terminators <b>end_do</b>, <b>end_for</b>, <b>end_function</b>, <b>end_if</b>, and <b>end_while</b>. These can be used to end the appropriate block type, but <b>end</b> can also be used to end any block.</p>
133 133
134 <p>Most statements in Luan are the same as Lua. Only those statements that differ will be listed here.</p> 134 <p>Most statements in Luan are the same as Lua. Only those statements that differ will be listed here.</p>
135 135
136 <h4 heading><a name="control">Control Structures</a></h4> 136 <h4 heading><a name="control" href="#control">Control Structures</a></h4>
137 137
138 <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> 138 <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>
139 139
140 <p>Luan does not have a <b>goto</b> statement.</p> 140 <p>Luan does not have a <b>goto</b> statement.</p>
141 141
142 <h4 heading><a name="for">For Statement</a></h4> 142 <h4 heading><a name="for" href="#for">For Statement</a></h4>
143 143
144 <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 <code>range</code> function in a generic <b>for</b> statement like this:</p> 144 <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 <code>range</code> function in a generic <b>for</b> statement like this:</p>
145 145
146 <pre> 146 <pre>
147 for i in range(from,to,step) do <em>block</em> end 147 for i in range(from,to,step) do <em>block</em> end
164 block 164 block
165 end 165 end
166 end 166 end
167 </pre> 167 </pre>
168 168
169 <h4 heading><a name="logical">Logical Statements</a></h4> 169 <h4 heading><a name="logical" href="#logical">Logical Statements</a></h4>
170 170
171 <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> 171 <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>
172 172
173 <pre> 173 <pre>
174 x==5 or error "x should be 5" 174 x==5 or error "x should be 5"
175 </pre> 175 </pre>
176 176
177 <h4 heading><a name="template_stmt">Template Statements</a></h4> 177 <h4 heading><a name="template_stmt" href="#template_stmt">Template Statements</a></h4>
178 178
179 <p>Template statements are a Luan addition that don't exist in Lua. See <a href="manual.html#template_stmt">Template Statements</a> in the Luan Reference Manual.</p> 179 <p>Template statements are a Luan addition that don't exist in Lua. See <a href="manual.html#template_stmt">Template Statements</a> in the Luan Reference Manual.</p>
180 180
181 181
182 <h3 heading><a name="expr">Expressions</a></h3> 182 <h3 heading><a name="expr" href="#expr">Expressions</a></h3>
183 183
184 <h4 heading><a name="conversions">Coercions and Conversions</a></h4> 184 <h4 heading><a name="conversions" href="#conversions">Coercions and Conversions</a></h4>
185 185
186 <p>Unlike Lua, Luan does not do automatic conversions of strings to numbers.</p> 186 <p>Unlike Lua, Luan does not do automatic conversions of strings to numbers.</p>
187 187
188 <h4 heading><a name="bit">Bitwise Operators</a></h4> 188 <h4 heading><a name="bit" href="#bit">Bitwise Operators</a></h4>
189 189
190 <p>Bitwise operators appear to be a 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> 190 <p>Bitwise operators appear to be a 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>
191 191
192 <h4 heading><a name="logical_ops">Logical Operators</a></h4> 192 <h4 heading><a name="logical_ops" href="#logical_ops">Logical Operators</a></h4>
193 193
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> 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>
195 195
196 <h4 heading><a name="concatenation">Concatenation</a></h4> 196 <h4 heading><a name="concatenation" href="#concatenation">Concatenation</a></h4>
197 197
198 <p>Unlike Lua, Luan converts all concatenation operands to strings. 198 <p>Unlike Lua, Luan converts all concatenation operands to strings.
199 199
200 <h4 heading><a name="constructors">Table Constructors</a></h4> 200 <h4 heading><a name="constructors" href="#constructors">Table Constructors</a></h4>
201 201
202 <p>Unlike Lua, Luan considers an <b>end_of_line</b> to be a field separator in a table constructor.</p> 202 <p>Unlike Lua, Luan considers an <b>end_of_line</b> to be a field separator in a table constructor.</p>
203 203
204 <h4 heading><a name="fn_calls">Function Calls</a></h4> 204 <h4 heading><a name="fn_calls" href="#fn_calls">Function Calls</a></h4>
205 205
206 <p>Unlike Lua, Luan does not allow extra non-nil arguments to be passed to a function. In Luan, this causes an error. This change helps find coding mistakes that would be very hard to detect otherwise.</p> 206 <p>Unlike Lua, Luan does not allow extra non-nil arguments to be passed to a function. In Luan, this causes an error. This change helps find coding mistakes that would be very hard to detect otherwise.</p>
207 207
208 <p>Luan does not support Lua's <code>v:name(args)</code> style object-oriented function call. Object oriented programming is done in Luan using closures, so this feature is not needed.</p> 208 <p>Luan does not support Lua's <code>v:name(args)</code> style object-oriented function call. Object oriented programming is done in Luan using closures, so this feature is not needed.</p>
209 209
210 <p>Luan doesn't support <em>proper tail calls</em>. Because Java doesn't support this cleanly, this was left out.</p> 210 <p>Luan doesn't support <em>proper tail calls</em>. Because Java doesn't support this cleanly, this was left out.</p>
211 211
212 <h4 heading><a name="template_expr">Template Expressions</a></h4> 212 <h4 heading><a name="template_expr" href="#template_expr">Template Expressions</a></h4>
213 213
214 <p>Template expressions are a Luan addition that don't exist in Lua. See <a href="manual.html#template_expr">Template Expressions</a> in the Luan Reference Manual.</p> 214 <p>Template expressions are a Luan addition that don't exist in Lua. See <a href="manual.html#template_expr">Template Expressions</a> in the Luan Reference Manual.</p>
215 215
216 </body> 216 </body>
217 </html> 217 </html>