If an external or built-in function detects an error of any kind, the language processor is informed, and a syntax error results. Execution of the clause that included the function call is, therefore, ended. Similarly, if an external function fails to return data correctly, the language processor detects this and reports it as an error.

If a syntax error occurs during the execution of an internal function, it can be trapped (using SIGNAL ON SYNTAX) and recovery may then be possible. If the error is not trapped, the program is ended.