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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
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7 * provide auxiliary C functions and macros to simplify iterating over both
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8 tables and iterator functions with the same statement.
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9
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10 This library completely ignores the ``__ipairs`` metamethod (as it is
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11 deprecated since Lua 5.3.0-alpha). It respects, however, any ``__index`` and
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12 ``__call`` metamethods (this may cause unexpected behavior when passing
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13 callable tables to ``ipairs``). The ``__call`` metamethod takes precedence over
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14 an existing ``__index`` metamethod.
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15
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16
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17
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18 Lua part of the library
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19 -----------------------
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20
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21 The new ``ipairs(...)`` function works as follows:
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22
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23 require "seqlua"
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24
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25 t = {"a", "b", "c"}
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26
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27 for i, v in ipairs(t) do
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28 print(i, v)
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29 end
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30 -- prints:
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31 -- 1 a
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32 -- 2 b
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33 -- 3 c
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34
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35 function alphabet()
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36 local letter = nil
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37 return function()
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38 if letter == nil then
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39 letter = "a"
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40 elseif letter == "z" then
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41 return nil
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42 else
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43 letter = string.char(string.byte(letter) + 1)
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44 end
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45 return letter
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46 end
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47 end
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48
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49 for i, v in ipairs(alphabet()) do
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50 print(i, v)
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51 end
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52 -- prints:
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53 -- 1 a
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54 -- 2 b
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55 -- 3 c
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56 -- ...
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57 -- 25 y
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58 -- 26 z
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59
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60 function filter(f, seq)
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61 return coroutine.wrap(function()
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62 for i, v in ipairs(seq) do f(v) end
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63 end)
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64 end
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65
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66 function filterfunc(v)
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67 local type_v = type(v)
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68 if type_v == "string" then
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69 coroutine.yield(v)
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70 elseif type_v == "number" then
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71 for i = 1, v do
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72 coroutine.yield(true)
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73 end
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74 end
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75 end
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76
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77 for v in filter(filterfunc, {"a", "b", 3, "c"}) do
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78 print(v)
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79 end
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80 -- prints:
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81 -- a
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82 -- b
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83 -- true
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84 -- true
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85 -- true
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86 -- c
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87
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88
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89 C part of the library
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90 ---------------------
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91
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92 In ``seqlualib.h``, the following macro is defined:
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93
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94 #define seqlua_iterloop(L, iter, idx) \
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95 for ( \
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96 seqlua_iterinit((L), (iter), (idx)); \
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97 seqlua_iternext(iter); \
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98 lua_pop((L), 1) \
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99 )
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100
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101 This macro allows iteration over either tables or iterator functions as the
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102 following example function demonstrates:
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103
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104 int printcsv(lua_State *L) {
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105 seqlua_Iterator iter;
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106 seqlua_iterloop(L, &iter, 1) {
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107 if (seqlua_itercount(&iter) > 1) fputs(",", stdout);
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108 fputs(luaL_tolstring(L, -1, NULL), stdout);
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109 lua_pop(L, 1); // pops value that luaL_tolstring pushed onto stack
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110 }
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111 fputs("\n", stdout);
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112 return 0;
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113 }
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114
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115 printcsv{"a", "b", "c"}
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116 -- prints: a,b,c
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117
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118 printcsv(assert(io.open("testfile")):lines())
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119 -- prints: line1,line2,... of "testfile"
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120
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121
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