seqlua
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Initial commit
| author | jbe |
|---|---|
| date | Wed Aug 20 00:39:10 2014 +0200 (2014-08-20) |
| parents | |
| children | 158dfce546c0 |
line source
1 seqlua: Extended sequences and iterators in Lua
2 ===============================================
4 This is an experimental package to extend Lua in the following manner:
6 * allow ipairs(...) to accept tables as well as functions or iterator triplets,
7 * provide a function iterator(...) that returns single functions unmodified,
8 but converts
9 * iterator triplets into closures, and
10 * tables into a function closure that iterates over the elements,
11 * provide the auxiliary C functions and macros to simplify iterating over both
12 tables and iterator functions with the same statement.
14 This library completely ignores the ``__ipairs`` metamethod (as it is
15 deprecated since Lua 5.3.0-alpha). It respects, however, any ``__call``
16 metamethods (this may cause unexpected behavior when passing callable tables
17 to ``ipairs``).
21 Lua part of the library
22 -----------------------
24 The new ``ipairs(...)`` function works as follows:
26 require "seqlua"
28 t = {"a", "b", "c"}
30 for i, v in ipairs(t) do
31 print(i, v)
32 end
33 -- prints:
34 -- 1 a
35 -- 2 b
36 -- 3 c
38 function alphabet()
39 local letter = nil
40 return function()
41 if letter == nil then
42 letter = "a"
43 elseif letter == "z" then
44 return nil
45 else
46 letter = string.char(string.byte(letter) + 1)
47 end
48 return letter
49 end
50 end
52 f = alphabet()
54 for i, v in ipairs(f) do
55 print(i, v)
56 end
57 -- prints:
58 -- 1 a
59 -- 2 b
60 -- 3 c
61 -- ...
62 -- 25 y
63 -- 26 z
65 set = {apple = true, banana = true}
66 for i, k, v in ipairs(pairs(set)) do
67 print(i, k, v)
68 end
69 -- prints:
70 -- 1 banana true
71 -- 2 apple true
72 -- (order of "apple" and "banana" may vary)
74 The function ``iterator(...)`` may be used to convert any table, any function,
75 or any iterator triplet into a single function (possibly creating a closure):
77 function filter_strings(...)
78 nextvalue = iterator(...)
79 return function()
80 local value
81 repeat
82 value = nextvalue()
83 until value == nil or type(value) == "string"
84 return value
85 end
86 end
88 for i, v in ipairs(filter_strings{"Hello", true, "World"}) do
89 print(i, v)
90 end
91 -- prints:
92 -- 1 Hello
93 -- 2 World
95 tbl = {apple = true, banana = true, [1] = "array entry"}
96 for v in filter_strings(pairs(tbl)) do
97 print(v)
98 end
99 -- prints:
100 -- banana
101 -- apple
102 -- (order may vary)
106 C part of the library
107 ---------------------
109 In ``seqlualib.h``, the following macro is defined:
111 #define seqlua_iterloop(L, iter, idx) \
112 for ( \
113 seqlua_iterinit((L), (iter), (idx)); \
114 seqlua_iternext(iter); \
115 lua_pop((L), 1) \
116 )
118 This macro allows iteration over either tables or iterator functions (but not
119 iterator triplets) as the following example function demonstrates:
121 int printcsv(lua_State *L) {
122 seqlua_Iterator iter;
123 seqlua_iterloop(L, &iter, 1) {
124 if (seqlua_itercount(&iter) > 1) fputs(",", stdout);
125 fputs(luaL_tolstring(L, -1, NULL), stdout);
126 lua_pop(L, 1);
127 }
128 fputs("\n", stdout);
129 return 0;
130 }
132 printcsv{"a", "b", "c"} -- prints: a,b,c
134 Additionally, ``seqlualib`` includes a function ``seqlua_iterclosure(L, idx)``,
135 which converts a table at a given stack index into a function closure (stored
136 on the same stack index) that iterates over the elements of the table. If the
137 value at the given stack index is already a function, it leaves the value
138 unchanged. If the value is convertible to a function using ``__ipairs,`` then
139 the function is replaced by its ``__ipairs`` metamethod.