annotate website/src/m.html.luan @ 1657:58d35500fdb3

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author Franklin Schmidt <fschmidt@gmail.com>
date Fri, 08 Apr 2022 09:16:52 -0600
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1 local Luan = require "luan:Luan.luan"
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2 local error = Luan.error
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3 local Io = require "luan:Io.luan"
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4 local Http = require "luan:http/Http.luan"
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5 local Shared = require "site:/lib/Shared.luan"
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6 local head = Shared.head or error()
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7 local docs_header = Shared.docs_header or error()
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8 local show_toc = Shared.show_toc or error()
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9 local show_content = Shared.show_content or error()
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10
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11
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12 local content = {
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13 intro = {
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14 title = "Introduction"
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15 content = function()
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16 %>
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17 <p>
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18 Luan is a high level programming language based on <a href="http://www.lua.org">Lua</a>. A great strength of Lua is its simplicity and Luan takes this even further, being even simpler than Lua. The goal is to provide a simple programming language for the casual programmer with as few concepts as possible so that one can quickly learn the language and then easily understand any code written in Luan.
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19 </p>
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20
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21 <p>
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22 Luan is implemented in Java and is tightly coupled with Java. So it makes a great scripting language for Java programmers.
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23 </p>
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24
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25 <p>
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26 Unlike Lua which is meant to be embedded, Luan is meant to be a full scripting language. This done not by adding features to Luan, but rather by providing a complete set of libraries.
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27 </p>
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28 <%
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29 end
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30 }
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31 basic = {
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32 title = "Basic Concepts"
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33 content = function()
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34 %>
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35 <p>
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36 This section describes the basic concepts of the language.
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37 </p>
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38 <%
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39 end
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40 subs = {
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41 types = {
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42 title = "Values and Types"
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43 content = function()
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44 %>
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45 <p>
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46 Luan is a <em>dynamically typed language</em>.
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47 This means that
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48 variables do not have types; only values do.
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49 There are no type definitions in the language.
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50 All values carry their own type.
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51 </p>
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52
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53 <p>
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54 All values in Luan are <em>first-class values</em>.
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55 This means that all values can be stored in variables,
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56 passed as arguments to other functions, and returned as results.
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57 </p>
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58
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59 <p>
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60 There are eight basic types in Luan:
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61 <em>nil</em>, <em>boolean</em>, <em>number</em>,
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62 <em>string</em>, <em>binary</em>, <em>function</em>, <em>java</em>,
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63 and <em>table</em>.
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64 <em>Nil</em> is the type of the value <b>nil</b>,
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65 whose main property is to be different from any other value;
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66 it usually represents the absence of a useful value.
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67 <em>Nil</em> is implemented as the Java value <em>null</em>.
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68 <em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
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69 <em>Boolean</em> is implemented as the Java class <em>Boolean</em>.
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70 <em>Number</em> represents both
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71 integer numbers and real (floating-point) numbers.
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72 <em>Number</em> is implemented as the Java class <em>Number</em>. Any Java subclass of <em>Number</em> is allowed and this is invisible to the Luan user. Operations on numbers follow the same rules of
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73 the underlying Java implementation.
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74 <em>String</em> is implemented as the Java class <em>String</em>.
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75 <em>Binary</em> is implemented as the Java type <em>byte[]</em>.
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76 </p>
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77
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78 <p>
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79 Luan can call (and manipulate) functions written in Luan and
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80 functions written in Java (see <a href="#fn_calls">Function Calls</a>).
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81 Both are represented by the type <em>function</em>.
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82 </p>
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83
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84 <p>
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85 The type <em>java</em> is provided to allow arbitrary Java objects to
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86 be stored in Luan variables.
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87 A <em>java</em> value is a Java object that isn't one of the standard Luan types.
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88 Java values have no predefined operations in Luan,
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89 except assignment and identity test.
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90 Java values are useful when Java access is enabled in Luan.
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91 </p>
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92
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93 <p>
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94 The type <em>table</em> implements associative arrays,
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95 that is, arrays that can be indexed not only with numbers,
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96 but with any Luan value except <b>nil</b>.
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97 Tables can be <em>heterogeneous</em>;
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98 that is, they can contain values of all types (except <b>nil</b>).
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99 Any key with value <b>nil</b> is not considered part of the table.
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100 Conversely, any key that is not part of a table has
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101 an associated value <b>nil</b>.
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102 </p>
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103
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104 <p>
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105 Tables are the sole data-structuring mechanism in Luan;
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106 they can be used to represent ordinary arrays, sequences,
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107 symbol tables, sets, records, graphs, trees, etc.
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108 To represent records, Luan uses the field name as an index.
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109 The language supports this representation by
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110 providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
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111 There are several convenient ways to create tables in Luan
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112 (see <a href="#constructors">Table Constructors</a>).
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113 </p>
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114
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115 <p>
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116 We use the term <em>sequence</em> to denote a table where
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117 the set of all positive numeric keys is equal to {1..<em>n</em>}
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118 for some non-negative integer <em>n</em>,
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119 which is called the length of the sequence (see <a href="#length">The Length Operator</a>).
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120 </p>
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121
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122 <p>
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123 Like indices,
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124 the values of table fields can be of any type.
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125 In particular,
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126 because functions are first-class values,
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127 table fields can contain functions.
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128 Thus tables can also carry <em>methods</em> (see <a href="#fn_def">Function Definitions</a>).
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129 </p>
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130
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131 <p>
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132 The indexing of tables follows
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133 the definition of raw equality in the language.
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134 The expressions <code>a[i]</code> and <code>a[j]</code>
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135 denote the same table element
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136 if and only if <code>i</code> and <code>j</code> are raw equal
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137 (that is, equal without metamethods).
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138 In particular, floats with integral values
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139 are equal to their respective integers
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140 (e.g., <code>1.0 == 1</code>).
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141 </p>
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142
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143 <p>
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144 Luan values are <em>objects</em>:
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145 variables do not actually <em>contain</em> values,
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146 only <em>references</em> to them.
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147 Assignment, parameter passing, and function returns
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148 always manipulate references to values;
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149 these operations do not imply any kind of copy.
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150 </p>
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151
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152 <p>
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153 The library function <a href="#Luan.type"><code>Luan.type</code></a> returns a string describing the type
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154 of a given value.
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155 </p>
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156 <%
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157 end
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158 }
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159 env = {
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160 title = "Environments"
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161 content = function()
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162 %>
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163 <p>
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164 The environment of a chunk starts with only one local variable: <code><a href="#require">require</a></code>. This function is used to load and access libraries and other modules. All other variables must be added to the environment using <a href="http://localhost:8080/manual.html#local_stmt">local declarations</a>.
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165 </p>
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166
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167 <p>
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168 As will be discussed in <a href="#vars">Variables</a> and <a href=#assignment">Assignment</a>,
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169 any reference to a free name
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170 (that is, a name not bound to any declaration) <code>var</code>
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171 can be syntactically translated to <code>_ENV.var</code> if <code>_ENV</code> is defined.
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172 </p>
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173 <%
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174 end
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175 }
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176 error = {
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177 title = "Error Handling"
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178 content = function()
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179 %>
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180 <p>
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181 Luan code can explicitly generate an error by calling the
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182 <a href="#Luan.error"><code>error</code></a> function.
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183 If you need to catch errors in Luan,
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184 you can use the <a href="#try">Try Statement</code></a>.
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185 </p>
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186
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187 <p>
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188 Whenever there is an error,
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189 an <em>error table</em>
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190 is propagated with information about the error.
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191 See <a href="#Luan.new_error"><code>Luan.new_error</code></a>.
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192 </p>
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193 <%
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194 end
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195 }
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196 meta = {
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197 title = "Metatables and Metamethods"
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198 content = function()
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199 %>
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200 <p>
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201 Every table in Luan can have a <em>metatable</em>.
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202 This <em>metatable</em> is an ordinary Luan table
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203 that defines the behavior of the original value
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204 under certain special operations.
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205 You can change several aspects of the behavior
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206 of operations over a value by setting specific fields in its metatable.
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207 For instance, when a table is the operand of an addition,
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208 Luan checks for a function in the field "<code>__add</code>" of the table's metatable.
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209 If it finds one,
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210 Luan calls this function to perform the addition.
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211 </p>
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212
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213 <p>
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214 The keys in a metatable are derived from the <em>event</em> names;
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215 the corresponding values are called <ii>metamethods</em>.
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216 In the previous example, the event is <code>"add"</code>
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217 and the metamethod is the function that performs the addition.
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218 </p>
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219
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220 <p>
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221 You can query the metatable of any table
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222 using the <a href="#Luan.get_metatable"><code>get_metatable</code></a> function.
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223 </p>
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224
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225 <p>
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226 You can replace the metatable of tables
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227 using the <a href="#Luan.set_metatable"><code>set_metatable</code></a> function.
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228 </p>
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229
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230 <p>
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231 A metatable controls how a table behaves in
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232 arithmetic operations, bitwise operations,
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233 order comparisons, concatenation, length operation, calls, and indexing.
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234 </p>
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235
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236 <p>
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237 A detailed list of events controlled by metatables is given next.
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238 Each operation is identified by its corresponding event name.
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239 The key for each event is a string with its name prefixed by
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240 two underscores, '<code>__</code>';
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241 for instance, the key for operation "add" is the
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242 string "<code>__add</code>".
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243 Note that queries for metamethods are always raw;
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244 the access to a metamethod does not invoke other metamethods.
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245 You can emulate how Luan queries a metamethod for an object <code>obj</code>
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246 with the following code:
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247 </p>
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248
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249 <pre>
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250 raw_get(get_metatable(obj) or {}, "__" .. event_name)
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251 </pre>
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252
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253 <p>
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254 Here are the events:
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255 </p>
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256
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257 <ul>
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258
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259 <li><p>
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260 <b>"add": </b>
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261 the <code>+</code> operation.
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262
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263 If any operand for an addition is a table,
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264 Luan will try to call a metamethod.
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265 First, Luan will check the first operand (even if it is valid).
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266 If that operand does not define a metamethod for the "<code>__add</code>" event,
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267 then Luan will check the second operand.
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268 If Luan can find a metamethod,
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269 it calls the metamethod with the two operands as arguments,
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270 and the result of the call
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271 (adjusted to one value)
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272 is the result of the operation.
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273 Otherwise,
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274 it raises an error.
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275 </p></li>
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276
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277 <li><p>
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278 <b>"sub": </b>
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279 the <code>-</code> operation.
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280 Behavior similar to the "add" operation.
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281 </li>
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282
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283 <li><p><b>"mul": </b>
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284 the <code>*</code> operation.
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285 Behavior similar to the "add" operation.
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286 </p></li>
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287
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288 <li><p>
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289 <b>"div": </b>
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290 the <code>/</code> operation.
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291 Behavior similar to the "add" operation.
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292 </p></li>
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293
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294 <li><p>
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295 <b>"mod": </b>
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296 the <code>%</code> operation.
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297 Behavior similar to the "add" operation.
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298 </p></li>
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299
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300 <li><p>
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301 <b>"pow": </b>
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302 the <code>^</code> (exponentiation) operation.
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303 Behavior similar to the "add" operation.
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304 </p></li>
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305
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306 <li><p>
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307 <b>"unm": </b>
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308 the <code>-</code> (unary minus) operation.
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309 Behavior similar to the "add" operation.
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310 </p></li>
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311
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312 <li><p>
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313 <b>"concat": </b>
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314 the <code>..</code> (concatenation) operation.
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315 Behavior similar to the "add" operation.
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316 </p></li>
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317
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318 <li><p>
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319 <b>"len": </b>
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320 the <code>#</code> (length) operation.
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321 If there is a metamethod,
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322 Luan calls it with the object as argument,
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323 and the result of the call
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324 (always adjusted to one value)
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325 is the result of the operation.
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326 If there is no metamethod but the object is a table,
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327 then Luan uses the table length operation (see <a href="#length">The Length Operator</a>).
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328 Otherwise, Luan raises an error.
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329 </p></li>
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330
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331 <li><p>
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332 <b>"eq": </b>
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333 the <code>==</code> (equal) operation.
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334 Behavior similar to the "add" operation,
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335 except that Luan will try a metamethod only when the values
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336 being compared are both tables
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337 and they are not primitively equal.
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338 The result of the call is always converted to a boolean.
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339 </p></li>
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340
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341 <li><p>
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342 <b>"lt": </b>
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343 the <code>&lt;</code> (less than) operation.
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344 Behavior similar to the "add" operation.
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345 The result of the call is always converted to a boolean.
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346 </p></li>
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347
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348 <li><p>
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349 <b>"le": </b>
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350 the <code>&lt;=</code> (less equal) operation.
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351 Unlike other operations,
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352 The less-equal operation can use two different events.
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353 First, Luan looks for the "<code>__le</code>" metamethod in both operands,
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354 like in the "lt" operation.
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355 If it cannot find such a metamethod,
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356 then it will try the "<code>__lt</code>" event,
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357 assuming that <code>a &lt;= b</code> is equivalent to <code>not (b &lt; a)</code>.
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358 As with the other comparison operators,
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359 the result is always a boolean.
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360 </p></li>
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361
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362 <li>
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363 <p>
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364 <b>"index": </b>
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365 The indexing access <code>table[key]</code>.
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366 This event happens
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367 when <code>key</code> is not present in <code>table</code>.
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368 The metamethod is looked up in <code>table</code>.
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369 </p>
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370
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371 <p>
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372 Despite the name,
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373 the metamethod for this event can be any type.
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374 If it is a function,
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375 it is called with <code>table</code> and <code>key</code> as arguments.
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376 Otherwise
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377 the final result is the result of indexing this metamethod object with <code>key</code>.
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378 (This indexing is regular, not raw,
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379 and therefore can trigger another metamethod if the metamethod object is a table.)
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380 </p>
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381 </li>
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382
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383 <li>
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384 <p>
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385 <b>"new_index": </b>
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386 The indexing assignment <code>table[key] = value</code>.
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387 Like the index event,
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388 this event happens when
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389 when <code>key</code> is not present in <code>table</code>.
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390 The metamethod is looked up in <code>table</code>.
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391 </p>
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392
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393 <p>
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394 Like with indexing,
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395 the metamethod for this event can be either a function or a table.
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396 If it is a function,
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397 it is called with <code>table</code>, <code>key</code>, and <code>value</code> as arguments.
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398 If it is a table,
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399 Luan does an indexing assignment to this table with the same key and value.
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400 (This assignment is regular, not raw,
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401 and therefore can trigger another metamethod.)
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402 </p>
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403
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404 <p>
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405 Whenever there is a "new_index" metamethod,
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406 Luan does not perform the primitive assignment.
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407 (If necessary,
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408 the metamethod itself can call <a href="#Luan.raw_set"><code>raw_set</code></a>
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409 to do the assignment.)
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410 </p>
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411 </li>
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412
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413 <li><p>
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414 <b>"gc":</b>
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415 This is when a table is garbage collected. When the table's <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#finalize()">finalize</a> method is called by the Java garbage collector, if there is a "<code>__gc</code>" metamethod then it is called with the table as a parameter.
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416 </p></li>
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417
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418 </ul>
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419 <%
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420 end
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421 }
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422 gc = {
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423 title = "Garbage Collection"
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424 content = function()
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425 %>
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426 <p>
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427 Luan uses Java's garbage collection.
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428 </p>
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429 <%
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430 end
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431 }
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432 }
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433 }
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434 lang = {
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435 title = "The Language"
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436 content = function()
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437 %>
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438 <p>
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439 This section describes the lexis, the syntax, and the semantics of Luan.
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440 In other words,
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441 this section describes
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442 which tokens are valid,
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443 how they can be combined,
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444 and what their combinations mean.
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445 </p>
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446
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447 <p>
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448 Language constructs will be explained using the usual extended BNF notation,
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449 in which
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450 {<em>a</em>}&nbsp;means&nbsp;0 or more <em>a</em>'s, and
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451 [<em>a</em>]&nbsp;means an optional <em>a</em>.
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452 Non-terminals are shown like non-terminal,
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453 keywords are shown like <b>kword</b>,
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454 and other terminal symbols are shown like &lsquo;<b>=</b>&rsquo;.
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455 The complete syntax of Luan can be found in <a href="#9">&sect;9</a>
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456 at the end of this manual.
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457 </p>
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458 <%
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459 end
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460 subs = {
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461 lex = {
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462 title = "Lexical Conventions"
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463 content = function()
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464 %>
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465 <p>
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466 Luan ignores spaces and comments
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467 between lexical elements (tokens),
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468 except as delimiters between names and keywords.
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469 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.
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470 </p>
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471
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472 <p>
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473 <em>Names</em>
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diff changeset
474 (also called <em>identifiers</em>)
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475 in Luan can be any string of letters,
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diff changeset
476 digits, and underscores,
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477 not beginning with a digit.
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478 Identifiers are used to name variables, table fields, and labels.
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479 </p>
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480
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481 <p>
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482 The following <em>keywords</em> are reserved
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483 and cannot be used as names:
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484 </p>
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485
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486 <p keywords>
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487 <span>and</span>
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488 <span>break</span>
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489 <span>catch</span>
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diff changeset
490 <span>continue</span>
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diff changeset
491 <span>do</span>
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492 <span>else</span>
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493 <span>elseif</span>
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494 <span>end_do</span>
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495 <span>end_for</span>
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496 <span>end_function</span>
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diff changeset
497 <span>end_if</span>
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diff changeset
498 <span>end_try</span>
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499 <span>end_while</span>
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diff changeset
500 <span>false</span>
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501 <span>finally</span>
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502 <span>for</span>
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503 <span>function</span>
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diff changeset
504 <span>if</span>
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diff changeset
505 <span>in</span>
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506 <span>local</span>
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507 <span>nil</span>
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508 <span>not</span>
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509 <span>or</span>
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510 <span>repeat</span>
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511 <span>return</span>
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512 <span>then</span>
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513 <span>true</span>
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514 <span>try</span>
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diff changeset
515 <span>until</span>
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516 <span>while</span>
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517 </p>
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518
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519 <p>
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diff changeset
520 Luan is a case-sensitive language:
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parents:
diff changeset
521 <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
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parents:
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522 are two different, valid names.
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diff changeset
523 </p>
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524
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diff changeset
525 <p>
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526 The following strings denote other tokens:
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527 </p>
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528
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529 <pre>
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diff changeset
530 + - * / % ^ #
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diff changeset
531 &amp; ~ | &lt;&lt; &gt;&gt; //
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532 == ~= &lt;= &gt;= &lt; &gt; =
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533 ( ) { } [ ] ::
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534 ; : , . .. ...
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535 </pre>
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536
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537 <p>
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538 <em>Literal strings</em>
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539 can be delimited by matching single or double quotes,
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540 and can contain the following C-like escape sequences:
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diff changeset
541 '<code>\a</code>' (bell),
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542 '<code>\b</code>' (backspace),
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parents:
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543 '<code>\f</code>' (form feed),
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544 '<code>\n</code>' (newline),
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545 '<code>\r</code>' (carriage return),
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parents:
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546 '<code>\t</code>' (horizontal tab),
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parents:
diff changeset
547 '<code>\v</code>' (vertical tab),
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548 '<code>\\</code>' (backslash),
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diff changeset
549 '<code>\"</code>' (quotation mark [double quote]),
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diff changeset
550 and '<code>\'</code>' (apostrophe [single quote]).
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parents:
diff changeset
551 A backslash followed by a real newline
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parents:
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552 results in a newline in the string.
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parents:
diff changeset
553 The escape sequence '<code>\z</code>' skips the following span
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554 of white-space characters,
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parents:
diff changeset
555 including line breaks;
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556 it is particularly useful to break and indent a long literal string
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parents:
diff changeset
557 into multiple lines without adding the newlines and spaces
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558 into the string contents.
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diff changeset
559 </p>
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diff changeset
560
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parents:
diff changeset
561 <p>
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parents:
diff changeset
562 Luan can specify any character in a literal string by its numerical value.
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parents:
diff changeset
563 This can be done
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diff changeset
564 with the escape sequence <code>\x<em>XX</em></code>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
565 where <em>XX</em> is a sequence of exactly two hexadecimal digits,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
566 or with the escape sequence <code>\u<em>XXXX</em></code>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
567 where <em>XXXX</em> is a sequence of exactly four hexadecimal digits,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
568 or with the escape sequence <code>\<em>ddd</em></code>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
569 where <em>ddd</em> is a sequence of up to three decimal digits.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
570 (Note that if a decimal escape sequence is to be followed by a digit,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
571 it must be expressed using exactly three digits.)
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
572 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
573
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
574 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
575 Literal strings can also be defined using a long format
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
576 enclosed by <em>long brackets</em>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
577 We define an <em>opening long bracket of level <em>n</em></em> as an opening
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
578 square bracket followed by <em>n</em> equal signs followed by another
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
579 opening square bracket.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
580 So, an opening long bracket of level 0 is written as <code>[[</code>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
581 an opening long bracket of level 1 is written as <code>[=[</code>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
582 and so on.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
583 A <em>closing long bracket</em> is defined similarly;
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
584 for instance,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
585 a closing long bracket of level 4 is written as <code>]====]</code>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
586 A <em>long literal</em> starts with an opening long bracket of any level and
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
587 ends at the first closing long bracket of the same level.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
588 It can contain any text except a closing bracket of the same level.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
589 Literals in this bracketed form can run for several lines,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
590 do not interpret any escape sequences,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
591 and ignore long brackets of any other level.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
592 Any kind of end-of-line sequence
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
593 (carriage return, newline, carriage return followed by newline,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
594 or newline followed by carriage return)
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
595 is converted to a simple newline.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
596 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
597
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
598 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
599 Any character in a literal string not
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
600 explicitly affected by the previous rules represents itself.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
601 However, Luan opens files for parsing in text mode,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
602 and the system file functions may have problems with
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
603 some control characters.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
604 So, it is safer to represent
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
605 non-text data as a quoted literal with
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
606 explicit escape sequences for non-text characters.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
607 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
608
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
609 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
610 For convenience,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
611 when the opening long bracket is immediately followed by a newline,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
612 the newline is not included in the string.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
613 As an example
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
614 the five literal strings below denote the same string:
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
615 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
616
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
617 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
618 a = 'alo\n123"'
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
619 a = "alo\n123\""
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
620 a = '\97lo\10\04923"'
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
621 a = [[alo
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
622 123"]]
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
623 a = [==[
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
624 alo
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
625 123"]==]
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
626 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
627
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
628 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
629 A <em>numerical constant</em> (or <em>numeral</em>)
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
630 can be written with an optional fractional part
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
631 and an optional decimal exponent,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
632 marked by a letter '<code>e</code>' or '<code>E</code>'.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
633 Luan also accepts hexadecimal constants,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
634 which start with <code>0x</code> or <code>0X</code>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
635 Hexadecimal constants also accept an optional fractional part
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
636 plus an optional binary exponent,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
637 marked by a letter '<code>p</code>' or '<code>P</code>'.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
638 A numeric constant with a fractional dot or an exponent
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
639 denotes a float;
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
640 otherwise it denotes an integer.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
641 Examples of valid integer constants are
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
642 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
643
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
644 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
645 3 345 0xff 0xBEBADA
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
646 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
647
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
648 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
649 Examples of valid float constants are
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
650 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
651
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
652 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
653 3.0 3.1416 314.16e-2 0.31416E1 34e1
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
654 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
655 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
656
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
657 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
658 A <em>comment</em> starts with a double hyphen (<code>--</code>)
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
659 anywhere outside a string.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
660 If the text immediately after <code>--</code> is not an opening long bracket,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
661 the comment is a <em>short comment</em>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
662 which runs until the end of the line.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
663 Otherwise, it is a <em>long comment</em>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
664 which runs until the corresponding closing long bracket.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
665 Long comments are frequently used to disable code temporarily.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
666 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
667 <%
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
668 end
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
669 }
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
670 vars = {
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
671 title = "Variables"
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
672 content = function()
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
673 %>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
674 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
675 Variables are places that store values.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
676 There are three kinds of variables in Luan:
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
677 global variables, local variables, and table fields.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
678 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
679
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
680 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
681 A single name can denote a global variable or a local variable
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
682 (or a function's formal parameter,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
683 which is a particular kind of local variable):
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
684 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
685
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
686 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
687 var ::= Name
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
688 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
689
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
690 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
691 Name denotes identifiers, as defined in <a href="#lex">Lexical Conventions</a>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
692 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
693
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
694 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
695 Local variables are <em>lexically scoped</em>:
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
696 local variables can be freely accessed by functions
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
697 defined inside their scope (see <a href="#visibility">Visibility Rules</a>).
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
698 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
699
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
700 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
701 Before the first assignment to a variable, its value is <b>nil</b>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
702 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
703
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
704 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
705 Square brackets are used to index a table:
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
706 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
707
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
708 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
709 var ::= prefixexp &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo;
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
710 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
711
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
712 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
713 The meaning of accesses to table fields can be changed via metatables.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
714 An access to an indexed variable <code>t[i]</code> is equivalent to
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
715 a call <code>gettable_event(t,i)</code>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
716 (See <a href="#meta">Metatables and Metamethods</a> for a complete description of the
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
717 <code>gettable_event</code> function.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
718 This function is not defined or callable in Luan.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
719 We use it here only for explanatory purposes.)
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
720 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
721
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
722 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
723 The syntax <code>var.Name</code> is just syntactic sugar for
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
724 <code>var["Name"]</code>:
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
725 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
726
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
727 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
728 var ::= prefixexp &lsquo;<b>.</b>&rsquo; Name
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
729 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
730
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
731 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
732 Global variables are not available by default. To enable global variable, you must define <code>_ENV</code> as a local variable whose value is a table. If <code>_ENV</code> is not defined, then an unrecognized variable name will produce a compile error. If <code>_ENV</code> is defined then an access to an unrecognized variable name will be consider a global variable. So then an acces to global variable <code>x</code>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
733 is equivalent to <code>_ENV.x</code>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
734 Due to the way that chunks are compiled,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
735 <code>_ENV</code> is never a global name (see <a href="#env">Environments</a>).
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
736 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
737 <%
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
738 end
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
739 }
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
740 stmt = {
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
741 title = "Statements"
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
742 content = function()
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
743 %>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
744 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
745 Luan supports an almost conventional set of statements,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
746 similar to those in Pascal or C.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
747 This set includes
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
748 assignments, control structures, function calls,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
749 and variable declarations.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
750 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
751 <%
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
752 end
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
753 subs = {
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parents:
diff changeset
754 blocks = {
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parents:
diff changeset
755 title = "Blocks"
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parents:
diff changeset
756 content = function()
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parents:
diff changeset
757 %>
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parents:
diff changeset
758 <p>
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parents:
diff changeset
759 A block is a list of statements,
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parents:
diff changeset
760 which are executed sequentially:
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parents:
diff changeset
761 </p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
762
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
763 <pre>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
764 block ::= {stat}
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
765 </pre>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
766
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
767 <p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
768 Luan has <em>empty statements</em>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
769 that allow you to separate statements with semicolons,
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
770 start a block with a semicolon
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
771 or write two semicolons in sequence:
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
772 </p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
773
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
774 <pre>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
775 stat ::= &lsquo;<b>;</b>&rsquo;
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
776 </pre>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
777
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
778 <p>
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parents:
diff changeset
779 A block can be explicitly delimited to produce a single statement:
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
780 </p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
781
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
782 <pre>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
783 stat ::= <b>do</b> block end_do
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
784 end_do ::= <b>end_do</b> | <b>end</b>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
785 </pre>
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parents:
diff changeset
786
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
787 <p>
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parents:
diff changeset
788 Explicit blocks are useful
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parents:
diff changeset
789 to control the scope of variable declarations.
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parents:
diff changeset
790 Explicit blocks are also sometimes used to
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parents:
diff changeset
791 add a <b>return</b> statement in the middle
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parents:
diff changeset
792 of another block (see <a href="#control">Control Structures</a>).
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parents:
diff changeset
793 </p>
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parents:
diff changeset
794 <%
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parents:
diff changeset
795 end
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parents:
diff changeset
796 }
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parents:
diff changeset
797 chunks = {
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parents:
diff changeset
798 title = "Chunks"
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parents:
diff changeset
799 content = function()
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parents:
diff changeset
800 %>
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parents:
diff changeset
801 <p>
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parents:
diff changeset
802 The unit of compilation of Luan is called a <em>chunk</em>.
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parents:
diff changeset
803 Syntactically,
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parents:
diff changeset
804 a chunk is simply a block:
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parents:
diff changeset
805 </p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
806
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parents:
diff changeset
807 <pre>
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parents:
diff changeset
808 chunk ::= block
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
809 </pre>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
810
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parents:
diff changeset
811 <p>
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parents:
diff changeset
812 Luan handles a chunk as the body of an anonymous function
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
813 with a variable number of arguments
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
814 (see <a href="#fn_def">Function Definitions</a>).
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parents:
diff changeset
815 As such, chunks can define local variables,
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
816 receive arguments, and return values.
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parents:
diff changeset
817 </p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
818
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
819 <p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
820 A chunk can be stored in a file or in a string inside the host program.
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
821 To execute a chunk,
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parents:
diff changeset
822 Luan first <em>loads</em> it,
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
823 compiling the chunk's code,
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parents:
diff changeset
824 and then Luan executes the compiled code.
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parents:
diff changeset
825 </p>
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parents:
diff changeset
826 <%
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parents:
diff changeset
827 end
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parents:
diff changeset
828 }
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
829 assignment = {
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
830 title = "Assignment"
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
831 content = function()
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parents:
diff changeset
832 %>
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parents:
diff changeset
833 <p>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
834 Luan allows multiple assignments.
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
835 Therefore, the syntax for assignment
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
836 defines a list of variables on the left side
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parents:
diff changeset
837 and a list of expressions on the right side.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
838 The elements in both lists are separated by commas:
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
839 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
840
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
841 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
842 stat ::= varlist &lsquo;<b>=</b>&rsquo; explist
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
843 varlist ::= var {&lsquo;<b>,</b>&rsquo; var}
540bf2343078 manual work
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parents:
diff changeset
844 explist ::= exp {&lsquo;<b>,</b>&rsquo; exp}
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
845 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
846
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
847 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
848 Expressions are discussed in <a href="#expressions">Expressions</a>.
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
849 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
850
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
851 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
852 Before the assignment,
540bf2343078 manual work
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parents:
diff changeset
853 the list of values is <em>adjusted</em> to the length of
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
854 the list of variables.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
855 If there are more values than needed,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
856 the excess values are thrown away.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
857 If there are fewer values than needed,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
858 the list is extended with as many <b>nil</b>'s as needed.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
859 If the list of expressions ends with a function call,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
860 then all values returned by that call enter the list of values,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
861 before the adjustment
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
862 (except when the call is enclosed in parentheses; see <a href="#expressions">Expressions</a>).
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
863 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
864
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
865 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
866 The assignment statement first evaluates all its expressions
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
867 and only then the assignments are performed.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
868 Thus the code
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
869 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
870
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
871 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
872 i = 3
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
873 i, a[i] = i+1, 20
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
874 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
875
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
876 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
877 sets <code>a[3]</code> to 20, without affecting <code>a[4]</code>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
878 because the <code>i</code> in <code>a[i]</code> is evaluated (to 3)
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
879 before it is assigned&nbsp;4.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
880 Similarly, the line
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
881 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
882
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
883 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
884 x, y = y, x
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
885 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
886
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
887 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
888 exchanges the values of <code>x</code> and <code>y</code>,
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
889 and
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
890 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
891
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
892 <pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
893 x, y, z = y, z, x
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
894 </pre>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
895
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
896 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
897 cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
898 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
899
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
900 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
901 The meaning of assignments to global variables
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
902 and table fields can be changed via metatables.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
903 An assignment to an indexed variable <code>t[i] = val</code> is equivalent to
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
904 <code>settable_event(t,i,val)</code>.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
905 (See <a href="#meta">Metatables and Metamethods</a> for a complete description of the
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
906 <code>settable_event</code> function.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
907 This function is not defined or callable in Luan.
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
908 We use it here only for explanatory purposes.)
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
909 </p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
910
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
911 <p>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
912 An assignment to a global name <code>x = val</code>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
913 is equivalent to the assignment
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
914 <code>_ENV.x = val</code> (see <a href="#env">Environments</a>).
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
915 Global names are only available when <code>_ENV</code> is defined.
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
916 </p>
540bf2343078 manual work
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parents:
diff changeset
917 <%
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parents:
diff changeset
918 end
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parents:
diff changeset
919 }
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
920 }
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
921 }
540bf2343078 manual work
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parents:
diff changeset
922 }
540bf2343078 manual work
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parents:
diff changeset
923 }
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
924 }
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
925
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
926
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
927 return function()
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parents:
diff changeset
928 Io.stdout = Http.response.text_writer()
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parents:
diff changeset
929 %>
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parents:
diff changeset
930 <!doctype html>
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parents:
diff changeset
931 <html>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
932 <head>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
933 <% head() %>
540bf2343078 manual work
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parents:
diff changeset
934 <title>Luan Reference Manual</title>
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parents:
diff changeset
935 <style>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
936 p[keywords] {
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
937 font-family: monospace;
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
938 margin-left: 40px;
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
939 max-width: 700px;
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
940 }
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
941 p[keywords] span {
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
942 display: inline-block;
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
943 width: 100px;
540bf2343078 manual work
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parents:
diff changeset
944 }
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parents:
diff changeset
945 </style>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
946 </head>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
947 <body>
540bf2343078 manual work
Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
948 <% docs_header() %>
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Franklin Schmidt <fschmidt@gmail.com>
parents:
diff changeset
949 <div content>
540bf2343078 manual work
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parents:
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950 <h1><a href="manual.html">Luan Reference Manual</a></h1>
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951 <p small>
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952 Original copyright &copy; 2015 Lua.org, PUC-Rio.
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953 Freely available under the terms of the
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954 <a href="http://www.lua.org/license.html">Lua license</a>.
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955 Modified for Luan.
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956 </p>
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957 <hr>
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958 <h2>Contents</h2>
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959 <div toc>
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960 <% show_toc(content) %>
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961 </div>
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962 <hr>
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963 <% show_content(content,2) %>
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964 </div>
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965 </body>
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966 </html>
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967 <%
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968 end