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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(seq)`` to accept tables as well as functions (i.e function
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7 iterators),
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8 * add a new function ``string.concat(separator, seq)`` to concat either table
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9 entries or function return values,
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10 * provide auxiliary C functions and macros to simplify iterating over both
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11 tables and iterator functions with the same statement.
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12
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13 In all cases, existing ``__index``, ``__len``, or ``__ipairs`` metamethods are
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14 respected. The ``__ipairs`` metamethod takes precedence.
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15
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16
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17 Lua part of the library
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18 -----------------------
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19
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20 The modified ``ipairs(seq)`` and the new ``string.concat(sep, seq)`` functions
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21 accept either a table or a function as ``seq``. This is demonstrated in the
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22 following examples:
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23
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24 require "seqlua"
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25
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26 t = {"a", "b", "c"}
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27
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28 for i, v in ipairs(t) do
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29 print(i, v)
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30 end
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31 -- prints:
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32 -- 1 a
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33 -- 2 b
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34 -- 3 c
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35
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36 print(string.concat(",", t))
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37 -- prints: a,b,c
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38
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39 function alphabet()
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40 local letter = nil
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41 return function()
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42 if letter == nil then
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43 letter = "a"
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44 elseif letter == "z" then
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45 return nil
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46 else
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47 letter = string.char(string.byte(letter) + 1)
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48 end
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49 return letter
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50 end
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51 end
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52
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53 for i, v in ipairs(alphabet()) do
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54 print(i, v)
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55 end
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56 -- prints:
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57 -- 1 a
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58 -- 2 b
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59 -- 3 c
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60 -- ...
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61 -- 25 y
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62 -- 26 z
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63
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64 print(string.concat(",", alphabet()))
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65 -- prints: a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z
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66
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67 function filter(f)
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68 return function(seq)
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69 return coroutine.wrap(function()
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70 for i, v in ipairs(seq) do f(v) end
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71 end)
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72 end
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73 end
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74
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75 alpha_beta_x = filter(function(v)
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76 if v == "a" then
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77 coroutine.yield("alpha")
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78 elseif v == "b" then
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79 coroutine.yield("beta")
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80 elseif type(v) == "number" then
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81 for i = 1, v do
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82 coroutine.yield("X")
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83 end
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84 end
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85 end)
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86
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87 print((","):concat(alpha_beta_x{"a", 3, "b", "c", "d"}))
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88 -- prints: alpha,X,X,X,beta
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89
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90 print((","):concat(alpha_beta_x(alphabet())))
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91 -- prints: alpha,beta
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92
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93
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94 C part of the library
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95 ---------------------
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96
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97 In ``seqlualib.h``, the following macro is defined:
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98
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99 #define seqlua_iterloop(L, iter, idx) \
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100 for ( \
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101 seqlua_iterinit((L), (iter), (idx)); \
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102 seqlua_iternext(iter); \
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103 )
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104
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105 and
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106
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107 #define seqlua_iterloopauto(L, iter, idx) \
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108 for ( \
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109 seqlua_iterinit((L), (iter), (idx)); \
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110 seqlua_iternext(iter); \
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111 lua_pop((L), 1) \
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112 )
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113
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114 This macro allows iteration over either tables or iterator functions as the
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115 following example function demonstrates:
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116
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117 int printcsv(lua_State *L) {
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118 seqlua_Iterator iter;
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119 seqlua_iterloop(L, &iter, 1) {
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120 if (seqlua_itercount(&iter) > 1) fputs(",", stdout);
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121 fputs(luaL_tolstring(L, -1, NULL), stdout);
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122 // two values need to be popped (the value pushed by
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123 // seqlua_iternext and the value pushed by luaL_tolstring)
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124 lua_pop(L, 2);
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125 }
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126 fputs("\n", stdout);
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127 return 0;
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128 }
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129
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130 printcsv{"a", "b", "c"}
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131 -- prints: a,b,c
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132
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133 printcsv(assert(io.open("testfile")):lines())
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134 -- prints: line1,line2,... of "testfile"
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135
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136
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