function blockgame.get_keys (tab)
	local keyset = {}
	local n = 0
	for key, value in pairs(tab) do
		n = n + 1
		keyset[n] = key
	end
	return keyset
end

function blockgame.shallow_copy_table (tab)
	local result = {}
	for key, value in pairs(tab) do
		result[key] = value
	end
	return result
end

function blockgame.shuffle (tab)
	local keys = blockgame.get_keys(tab)
	local result = {}
	while #keys > 0 do
		local index = math.random(1, #keys)
		local key = table.remove(keys, index)
		table.insert(result, tab[key])
	end
	return result
end