util/iterators.lua

   1 -- Prosody IM
   2 -- Copyright (C) 2008-2010 Matthew Wild
   3 -- Copyright (C) 2008-2010 Waqas Hussain
   4 --
   5 -- This project is MIT/X11 licensed. Please see the
   6 -- COPYING file in the source package for more information.
   7 --
   8
   9 --[[ Iterators ]]--
  10
  11 local it = {};
  12
  13 local t_insert = table.insert;
  14 local select, next = select, next;
  15 local unpack = table.unpack or unpack; --luacheck: ignore 113 143
  16 local pack = table.pack or function (...) return { n = select("#", ...), ... }; end -- luacheck: ignore 143
  17 local type = type;
  18 local table, setmetatable = table, setmetatable;
  19
  20 local _ENV = nil;
  21 --luacheck: std none
  22
  23 -- Reverse an iterator
  24 function it.reverse(f, s, var)
  25         local results = {};
  26
  27         -- First call the normal iterator
  28         while true do
  29                 local ret = { f(s, var) };
  30                 var = ret[1];
  31                 if var == nil then break; end
  32                 t_insert(results, 1, ret);
  33         end
  34
  35         -- Then return our reverse one
  36         local i,max = 0, #results;
  37         return function (_results)
  38                 if i<max then
  39                         i = i + 1;
  40                         return unpack(_results[i]);
  41                 end
  42         end, results;
  43 end
  44
  45 -- Iterate only over keys in a table
  46 local function _keys_it(t, key)
  47         return (next(t, key));
  48 end
  49 function it.keys(t)
  50         return _keys_it, t;
  51 end
  52
  53 -- Iterate only over values in a table
  54 function it.values(t)
  55         local key, val;
  56         return function (_t)
  57                 key, val = next(_t, key);
  58                 return val;
  59         end, t;
  60 end
  61
  62 -- Iterate over the n:th return value
  63 function it.select(n, f, s, var)
  64         return function (_s)
  65                 local ret = pack(f(_s, var));
  66                 var = ret[1];
  67                 return ret[n];
  68         end, s, var;
  69 end
  70
  71 -- Given an iterator, iterate only over unique items
  72 function it.unique(f, s, var)
  73         local set = {};
  74
  75         return function ()
  76                 while true do
  77                         local ret = pack(f(s, var));
  78                         var = ret[1];
  79                         if var == nil then break; end
  80                         if not set[var] then
  81                                 set[var] = true;
  82                                 return unpack(ret, 1, ret.n);
  83                         end
  84                 end
  85         end;
  86 end
  87
  88 --[[ Return the number of items an iterator returns ]]--
  89 function it.count(f, s, var)
  90         local x = 0;
  91
  92         while true do
  93                 var = f(s, var);
  94                 if var == nil then break; end
  95                 x = x + 1;
  96         end
  97
  98         return x;
  99 end
 100
 101 -- Return the first n items an iterator returns
 102 function it.head(n, f, s, var)
 103         local c = 0;
 104         return function (_s, _var)
 105                 if c >= n then
 106                         return nil;
 107                 end
 108                 c = c + 1;
 109                 return f(_s, _var);
 110         end, s, var;
 111 end
 112
 113 -- Skip the first n items an iterator returns
 114 function it.skip(n, f, s, var)
 115         for _ = 1, n do
 116                 var = f(s, var);
 117         end
 118         return f, s, var;
 119 end
 120
 121 -- Return the last n items an iterator returns
 122 function it.tail(n, f, s, var)
 123         local results, count = {}, 0;
 124         while true do
 125                 local ret = pack(f(s, var));
 126                 var = ret[1];
 127                 if var == nil then break; end
 128                 results[(count%n)+1] = ret;
 129                 count = count + 1;
 130         end
 131
 132         if n > count then n = count; end
 133
 134         local pos = 0;
 135         return function ()
 136                 pos = pos + 1;
 137                 if pos > n then return nil; end
 138                 local ret = results[((count-1+pos)%n)+1];
 139                 return unpack(ret, 1, ret.n);
 140         end
 141         --return reverse(head(n, reverse(f, s, var))); -- !
 142 end
 143
 144 function it.filter(filter, f, s, var)
 145         if type(filter) ~= "function" then
 146                 local filter_value = filter;
 147                 function filter(x) return x ~= filter_value; end
 148         end
 149         return function (_s, _var)
 150                 local ret;
 151                 repeat ret = pack(f(_s, _var));
 152                         _var = ret[1];
 153                 until _var == nil or filter(unpack(ret, 1, ret.n));
 154                 return unpack(ret, 1, ret.n);
 155         end, s, var;
 156 end
 157
 158 local function _ripairs_iter(t, key) if key > 1 then return key-1, t[key-1]; end end
 159 function it.ripairs(t)
 160         return _ripairs_iter, t, #t+1;
 161 end
 162
 163 local function _range_iter(max, curr) if curr < max then return curr + 1; end end
 164 function it.range(x, y)
 165         if not y then x, y = 1, x; end -- Default to 1..x if y not given
 166         return _range_iter, y, x-1;
 167 end
 168
 169 -- Convert the values returned by an iterator to an array
 170 function it.to_array(f, s, var)
 171         local t = {};
 172         while true do
 173                 var = f(s, var);
 174                 if var == nil then break; end
 175                 t_insert(t, var);
 176         end
 177         return t;
 178 end
 179
 180 function it.sorted_pairs(t, sort_func)
 181         local keys = it.to_array(it.keys(t));
 182         table.sort(keys, sort_func);
 183         local i = 0;
 184         return function ()
 185                 i = i + 1;
 186                 local key = keys[i];
 187                 if key ~= nil then
 188                         return key, t[key];
 189                 end
 190         end;
 191 end
 192
 193 -- Treat the return of an iterator as key,value pairs,
 194 -- and build a table
 195 function it.to_table(f, s, var)
 196         local t, var2 = {};
 197         while true do
 198                 var, var2 = f(s, var);
 199                 if var == nil then break; end
 200                 t[var] = var2;
 201         end
 202         return t;
 203 end
 204
 205 local function _join_iter(j_s, j_var)
 206         local iterators, current_idx = j_s[1], j_s[2];
 207         local f, s, var = unpack(iterators[current_idx], 1, 3);
 208         if j_var ~= nil then
 209                 var = j_var;
 210         end
 211         local ret = pack(f(s, var));
 212         local var1 = ret[1];
 213         if var1 == nil then
 214                 -- End of this iterator, advance to next
 215                 if current_idx == #iterators then
 216                         -- No more iterators, return nil
 217                         return;
 218                 end
 219                 j_s[2] = current_idx + 1;
 220                 return _join_iter(j_s);
 221         end
 222         return unpack(ret, 1, ret.n);
 223 end
 224 local join_methods = {};
 225 local join_mt = {
 226         __index = join_methods;
 227         __call = function (t, s, var) --luacheck: ignore 212/t
 228                 return _join_iter(s, var);
 229         end;
 230 };
 231
 232 function join_methods:append(f, s, var)
 233         table.insert(self, { f, s, var });
 234         return self, { self, 1 };
 235 end
 236
 237 function join_methods:prepend(f, s, var)
 238         table.insert(self, { f, s, var }, 1);
 239         return self, { self, 1 };
 240 end
 241
 242 function it.join(f, s, var)
 243         return setmetatable({ {f, s, var} }, join_mt);
 244 end
 245
 246 return it;