seqlua
view README @ 11:814d42156b14
Extended README to contain example for file:lines() iterator
| author | jbe |
|---|---|
| date | Wed Aug 20 04:54:49 2014 +0200 (2014-08-20) |
| parents | bb2cf91174ac |
| children | 91b0d0d4c4dd |
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 d
78 -- 5 e
79 -- 6 f
81 set = {apple = true, banana = true}
82 for i, k, v in ipairs(pairs(set)) do
83 print(i, k, v)
84 end
85 -- prints:
86 -- 1 banana true
87 -- 2 apple true
88 -- (order of "apple" and "banana" may vary)
90 The function ``iterator(...)`` may be used to convert any table, any function,
91 or any iterator triplet into a single function (possibly creating a closure):
93 require "seqlua"
95 function filter_strings(...)
96 nextvalue = iterator(...)
97 return function()
98 local value
99 repeat
100 value = nextvalue()
101 until value == nil or type(value) == "string"
102 return value
103 end
104 end
106 for i, v in ipairs(filter_strings{"Hello", true, "World"}) do
107 print(i, v)
108 end
109 -- prints:
110 -- 1 Hello
111 -- 2 World
113 tbl = {apple = true, banana = true, [1] = "array entry"}
114 for v in filter_strings(pairs(tbl)) do
115 print(v)
116 end
117 -- prints:
118 -- banana
119 -- apple
120 -- (order may vary)
124 C part of the library
125 ---------------------
127 In ``seqlualib.h``, the following macro is defined:
129 #define seqlua_iterloop(L, iter, idx) \
130 for ( \
131 seqlua_iterinit((L), (iter), (idx)); \
132 seqlua_iternext(iter); \
133 lua_pop((L), 1) \
134 )
136 This macro allows iteration over either tables or iterator functions (but not
137 iterator triplets) as the following example function demonstrates:
139 int printcsv(lua_State *L) {
140 seqlua_Iterator iter;
141 seqlua_iterloop(L, &iter, 1) {
142 if (seqlua_itercount(&iter) > 1) fputs(",", stdout);
143 fputs(luaL_tolstring(L, -1, NULL), stdout);
144 lua_pop(L, 1); // pops value that luaL_tolstring pushed onto stack
145 }
146 fputs("\n", stdout);
147 return 0;
148 }
150 printcsv{"a", "b", "c"}
151 -- prints: a,b,c
153 printcsv(assert(io.open("testfile")):lines())
154 -- prints: line1,line2,... of "testfile"
156 NOTE: ``seqlua_iterinit`` will store one extra element on the stack during
157 iteration. When ``seqlua_iternext`` returns 0, this extra element is popped
158 from the stack automatically.
160 Additionally, ``seqlualib`` includes a function ``seqlua_iterclosure(L, idx)``,
161 which converts a table at a given stack index into a function closure (stored
162 on the same stack index) that iterates over the elements of the table. If the
163 value at the given stack index is already a function, it leaves the value
164 unchanged. If the value is convertible to a function using ``__call,`` then the
165 value is replaced by a closure calling the ``__call`` metamethod.