-- Homework 23, problem 3: Safe lookup.
--
-- Define `local function lookup(dict, key)` that returns the value
-- if the key exists or the string "(not found)" if it does not.
-- Test with three calls covering hit, miss, and a key held in a
-- variable.
--
-- Run with: lua exercises/23/homework/03-safe-lookup.lua

-- Your code goes here: