4.2.1 Errors While Executing Statements

Statements do not return values, but some kinds of statements can, under certain circumstances described below, generate errors. If such an error is generated in a verb whose `d' (debug) bit is not set, then the error is ignored and the statement that generated it is simply skipped; execution proceeds with the next statement.

This error-ignoring behavior is very error prone, since it affects all errors, including ones the programmer may not have anticipated. The `d' bit exists only for historical reasons; it was once the only way for MOO programmers to catch and handle errors. The error-catching expression and the try-except statement are far better ways of accomplishing the same thing.

If the `d' bit is set, as it usually is, then the error is raised and can be caught and handled either by code surrounding the expression in question or by verbs higher up on the chain of calls leading to the current verb. If the error is not caught, then the server aborts the entire task and, by default, prints a message to the current player. See the descriptions of the error-catching expression and the try-except statement for the details of how errors can be caught, and the chapter on server assumptions about the database for details on the handling of uncaught errors.