util.iterators: New iterators library

diff --git a/util/iterators.lua b/util/iterators.lua
new file mode 100644 (file)
index 0000000..7c9b526
--- /dev/null
+++ b/util/iterators.lua
@@ -0,0 +1,94 @@
+--[[ Iterators ]]--
+
+-- Reverse an iterator
+function reverse(f, s, var)
+       local results = {};
+
+       -- First call the normal iterator
+       while true do
+               local ret = { f(s, var) };
+               var = ret[1];
+               if var == nil then break; end
+               table.insert(results, 1, ret);
+       end
+       
+       -- Then return our reverse one
+       local i,max = 0, #results;
+       return function (results)
+                       if i<max then
+                               i = i + 1;
+                               return unpack(results[i]);
+                       end
+               end, results;
+end
+
+-- Iterate only over keys in a table
+local function _keys_it(t, key)
+       return (next(t, key));
+end
+function keys(t)
+       return _keys_it, t;
+end
+
+-- Iterate only over values in a table
+function values(t)
+       local key, val;
+       return function (t)
+               key, val = next(t, key);
+               return val;
+       end, t;
+end
+
+-- Given an iterator, iterate only over unique items
+function unique(f, s, var)
+       local set = {};
+       
+       return function ()
+               while true do
+                       local ret = { f(s, var) };
+                       var = ret[1];
+                       if var == nil then break; end
+                       if not set[var] then
+                               set[var] = true;
+                               return var;
+                       end
+               end
+       end;
+end
+
+--[[ Return the number of items an iterator returns ]]--
+function count(f, s, var)
+       local x = 0;
+       
+       while true do
+               local ret = { f(s, var) };
+               var = ret[1];
+               if var == nil then break; end
+               x = x + 1;
+       end     
+       
+       return x;
+end
+
+-- Convert the values returned by an iterator to an array
+function it2array(f, s, var)
+       local t, var = {};
+       while true do
+               var = f(s, var);
+               if var == nil then break; end
+               table.insert(t, var);
+       end
+       return t;
+end
+
+-- Treat the return of an iterator as key,value pairs, 
+-- and build a table
+function it2table(f, s, var)
+       local t, var = {};
+       while true do
+               var, var2 = f(s, var);
+               if var == nil then break; end
+               t[var] = var2;
+       end
+       return t;
+end