+ --return reverse(head(n, reverse(f, s, var))); -- !
+end
+
+function it.filter(filter, f, s, var)
+ if type(filter) ~= "function" then
+ local filter_value = filter;
+ function filter(x) return x ~= filter_value; end
+ end
+ return function (s, var)
+ local ret;
+ repeat ret = pack(f(s, var));
+ var = ret[1];
+ until var == nil or filter(unpack(ret, 1, ret.n));
+ return unpack(ret, 1, ret.n);
+ end, s, var;
+end
+
+local function _ripairs_iter(t, key) if key > 1 then return key-1, t[key-1]; end end
+function it.ripairs(t)
+ return _ripairs_iter, t, #t+1;
+end
+
+local function _range_iter(max, curr) if curr < max then return curr + 1; end end
+function it.range(x, y)
+ if not y then x, y = 1, x; end -- Default to 1..x if y not given
+ return _range_iter, y, x-1;