Donkey provides convenient error handling capabilities. When an error is encountered while stepping (using either Step or Step All), the error description is displayed in the message area (Section 2.4), and in addition, the expression that produced the error is placed in the evaluation area . At this point, the user may perform actions associated with step mode including Unstep.
A useful method for debugging is to initially set the Breakpoints option to Applications and then Step All. When an error is encountered, the last function call made before the error is displayed in the evaluation area. One can then change the Breakpoints option to All and step one reduction at a time until the error is encountered at a finer granularity.