prosody
75b8afb79143
util/iterators.lua

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util/iterators.lua @ 919:75b8afb79143

util.iterators: New iterators library
author Matthew Wild <mwild1@gmail.com>
date Wed, 25 Mar 2009 03:01:10 +0000
child 1522:569d58d21612
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918:967edf874df7 919:75b8afb79143
1 --[[ Iterators ]]--
2
3 -- Reverse an iterator
4 function reverse(f, s, var)
5 local results = {};
6
7 -- First call the normal iterator
8 while true do
9 local ret = { f(s, var) };
10 var = ret[1];
11 if var == nil then break; end
12 table.insert(results, 1, ret);
13 end
14
15 -- Then return our reverse one
16 local i,max = 0, #results;
17 return function (results)
18 if i<max then
19 i = i + 1;
20 return unpack(results[i]);
21 end
22 end, results;
23 end
24
25 -- Iterate only over keys in a table
26 local function _keys_it(t, key)
27 return (next(t, key));
28 end
29 function keys(t)
30 return _keys_it, t;
31 end
32
33 -- Iterate only over values in a table
34 function values(t)
35 local key, val;
36 return function (t)
37 key, val = next(t, key);
38 return val;
39 end, t;
40 end
41
42 -- Given an iterator, iterate only over unique items
43 function unique(f, s, var)
44 local set = {};
45
46 return function ()
47 while true do
48 local ret = { f(s, var) };
49 var = ret[1];
50 if var == nil then break; end
51 if not set[var] then
52 set[var] = true;
53 return var;
54 end
55 end
56 end;
57 end
58
59 --[[ Return the number of items an iterator returns ]]--
60 function count(f, s, var)
61 local x = 0;
62
63 while true do
64 local ret = { f(s, var) };
65 var = ret[1];
66 if var == nil then break; end
67 x = x + 1;
68 end
69
70 return x;
71 end
72
73 -- Convert the values returned by an iterator to an array
74 function it2array(f, s, var)
75 local t, var = {};
76 while true do
77 var = f(s, var);
78 if var == nil then break; end
79 table.insert(t, var);
80 end
81 return t;
82 end
83
84 -- Treat the return of an iterator as key,value pairs,
85 -- and build a table
86 function it2table(f, s, var)
87 local t, var = {};
88 while true do
89 var, var2 = f(s, var);
90 if var == nil then break; end
91 t[var] = var2;
92 end
93 return t;
94 end