The halt and trace functions raise a REXX HALT condition or change the REXX interactive debug mode while a REXX procedure is running. These interfaces may be preferred over the RXHLT and RXTRC system exits. The system exits require an additional call to an exit routine after each REXX instruction completes. This might cause a noticeable performance degradation. The halt and trace functions are a single request to change the halt or trace state and do not degrade the REXX procedure performance.