Even if it were practical for implementers [of a language -smj] never to provoke an error and thus provide an idyllic world from which error had been banished, that design would still have a major drawback because the goal of a program is not so much to avoid committing errors but rather to fulfil its duty. In that sense, an error is a kind of crude guard rail: when we encounter it, it shows us that the program is not going as we intended. Errors and erroneous contexts need to be pointed out as early as possible so that their source can be corrected as soon as possible.