seqlua
view README @ 8:144f0bddee2b
Pass value as argument to __call metamethod
| author | jbe |
|---|---|
| date | Wed Aug 20 04:24:08 2014 +0200 (2014-08-20) |
| parents | 2cb22d01fdd0 |
| children | bb2cf91174ac |
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(from, to)
39 local letter = nil
40 return function()
41 if letter == nil then
42 letter = from
43 elseif letter == to 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("a", "z")
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 c = setmetatable(
66 { iter = alphabet("a", "f") },
67 { __call = function(t) return t.iter() end }
68 )
70 for i, v in ipairs(c) do
71 print(i, v)
72 end
73 -- prints:
74 -- 1 a
75 -- 2 b
76 -- 3 c
77 -- 4 e
78 -- 5 f
80 set = {apple = true, banana = true}
81 for i, k, v in ipairs(pairs(set)) do
82 print(i, k, v)
83 end
84 -- prints:
85 -- 1 banana true
86 -- 2 apple true
87 -- (order of "apple" and "banana" may vary)
89 The function ``iterator(...)`` may be used to convert any table, any function,
90 or any iterator triplet into a single function (possibly creating a closure):
92 require "seqlua"
94 function filter_strings(...)
95 nextvalue = iterator(...)
96 return function()
97 local value
98 repeat
99 value = nextvalue()
100 until value == nil or type(value) == "string"
101 return value
102 end
103 end
105 for i, v in ipairs(filter_strings{"Hello", true, "World"}) do
106 print(i, v)
107 end
108 -- prints:
109 -- 1 Hello
110 -- 2 World
112 tbl = {apple = true, banana = true, [1] = "array entry"}
113 for v in filter_strings(pairs(tbl)) do
114 print(v)
115 end
116 -- prints:
117 -- banana
118 -- apple
119 -- (order may vary)
123 C part of the library
124 ---------------------
126 In ``seqlualib.h``, the following macro is defined:
128 #define seqlua_iterloop(L, iter, idx) \
129 for ( \
130 seqlua_iterinit((L), (iter), (idx)); \
131 seqlua_iternext(iter); \
132 lua_pop((L), 1) \
133 )
135 This macro allows iteration over either tables or iterator functions (but not
136 iterator triplets) as the following example function demonstrates:
138 int printcsv(lua_State *L) {
139 seqlua_Iterator iter;
140 seqlua_iterloop(L, &iter, 1) {
141 if (seqlua_itercount(&iter) > 1) fputs(",", stdout);
142 fputs(luaL_tolstring(L, -1, NULL), stdout);
143 lua_pop(L, 1); // pops value that luaL_tolstring pushed onto stack
144 }
145 fputs("\n", stdout);
146 return 0;
147 }
149 printcsv{"a", "b", "c"} -- prints: a,b,c
151 NOTE: ``seqlua_iterinit`` will store one extra element on the stack during
152 iteration. When ``seqlua_iternext`` returns 0, this extra element is popped
153 from the stack automatically.
155 Additionally, ``seqlualib`` includes a function ``seqlua_iterclosure(L, idx)``,
156 which converts a table at a given stack index into a function closure (stored
157 on the same stack index) that iterates over the elements of the table. If the
158 value at the given stack index is already a function, it leaves the value
159 unchanged. If the value is convertible to a function using ``__call,`` then the
160 value is replaced by a closure calling the ``__call`` metamethod.