--[[ 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