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1 seqlua: Extended sequences and iterators in Lua
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2 ===============================================
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3
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4 This is an experimental package to extend Lua in the following manner:
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5
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6 * allow ipairs(...) to accept tables as well as functions or iterator triplets,
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7 * provide a function iterator(...) that returns single functions unmodified,
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8 but converts
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9 * iterator triplets into closures, and
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10 * tables into a function closure that iterates over the elements,
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11 * provide the auxiliary C functions and macros to simplify iterating over both
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12 tables and iterator functions with the same statement.
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13
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14 This library completely ignores the ``__ipairs`` metamethod (as it is
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15 deprecated since Lua 5.3.0-alpha). It respects, however, any ``__call``
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16 metamethods (this may cause unexpected behavior when passing callable tables
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17 to ``ipairs``).
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18
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19
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20
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21 Lua part of the library
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22 -----------------------
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23
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24 The new ``ipairs(...)`` function works as follows:
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25
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26 require "seqlua"
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27
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28 t = {"a", "b", "c"}
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29
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30 for i, v in ipairs(t) do
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31 print(i, v)
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32 end
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33 -- prints:
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34 -- 1 a
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35 -- 2 b
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36 -- 3 c
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37
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38 function alphabet()
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39 local letter = nil
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40 return function()
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41 if letter == nil then
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42 letter = "a"
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43 elseif letter == "z" then
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44 return nil
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45 else
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46 letter = string.char(string.byte(letter) + 1)
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47 end
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48 return letter
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49 end
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50 end
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51
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52 f = alphabet()
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53
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54 for i, v in ipairs(f) do
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55 print(i, v)
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56 end
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57 -- prints:
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58 -- 1 a
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59 -- 2 b
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60 -- 3 c
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61 -- ...
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62 -- 25 y
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63 -- 26 z
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64
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65 set = {apple = true, banana = true}
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66 for i, k, v in ipairs(pairs(set)) do
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67 print(i, k, v)
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68 end
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69 -- prints:
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70 -- 1 banana true
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71 -- 2 apple true
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72 -- (order of "apple" and "banana" may vary)
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73
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74 The function ``iterator(...)`` may be used to convert any table, any function,
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75 or any iterator triplet into a single function (possibly creating a closure):
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76
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77 require "seqlua"
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78
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79 function filter_strings(...)
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80 nextvalue = iterator(...)
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81 return function()
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82 local value
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83 repeat
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84 value = nextvalue()
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85 until value == nil or type(value) == "string"
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86 return value
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87 end
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88 end
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89
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90 for i, v in ipairs(filter_strings{"Hello", true, "World"}) do
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91 print(i, v)
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92 end
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93 -- prints:
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94 -- 1 Hello
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95 -- 2 World
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96
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97 tbl = {apple = true, banana = true, [1] = "array entry"}
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98 for v in filter_strings(pairs(tbl)) do
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99 print(v)
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100 end
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101 -- prints:
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102 -- banana
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103 -- apple
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104 -- (order may vary)
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105
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106
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107
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108 C part of the library
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109 ---------------------
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110
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111 In ``seqlualib.h``, the following macro is defined:
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112
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113 #define seqlua_iterloop(L, iter, idx) \
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114 for ( \
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115 seqlua_iterinit((L), (iter), (idx)); \
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116 seqlua_iternext(iter); \
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117 lua_pop((L), 1) \
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118 )
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119
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120 This macro allows iteration over either tables or iterator functions (but not
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121 iterator triplets) as the following example function demonstrates:
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122
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123 int printcsv(lua_State *L) {
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124 seqlua_Iterator iter;
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125 seqlua_iterloop(L, &iter, 1) {
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126 if (seqlua_itercount(&iter) > 1) fputs(",", stdout);
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127 fputs(luaL_tolstring(L, -1, NULL), stdout);
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128 lua_pop(L, 1); // pops value that luaL_tolstring pushed onto stack
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129 }
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130 fputs("\n", stdout);
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131 return 0;
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132 }
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133
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134 printcsv{"a", "b", "c"} -- prints: a,b,c
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135
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136 NOTE: If the index passed to ``seqlua_iterinit`` points to a value that has a
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137 ``__call`` metamethod, then the value at the stack position will be replaced by
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138 that metamethod.
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139
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140 Additionally, ``seqlualib`` includes a function ``seqlua_iterclosure(L, idx)``,
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141 which converts a table at a given stack index into a function closure (stored
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142 on the same stack index) that iterates over the elements of the table. If the
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143 value at the given stack index is already a function, it leaves the value
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144 unchanged. If the value is convertible to a function using ``__call,`` then the
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145 value is replaced by its ``__call`` metamethod.
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146
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147
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