Delaying Goals

(16th-July-2020)

• One of the most useful abilities of a meta-interpreter is to delay goals. Some goals, rather than being proved, can be collected in a list. At the end of the proof, the system derives the implication that, if the delayed goals were all true, the computed answer would be true.

• A number of reasons exist for providing a facility for collecting goals that should be delayed:

• to implement consistency-based diagnosis and abduction, the assumables are delayed;

• to delay subgoals with variables, in the hope that subsequent calls will ground the variables; and

• to create new rules that leave out intermediate steps - for example, if the delayed goals are to be asked of a user or queried from a database. This is called partial evaluation and is used for explanation-based learning to leave out intermediate steps in a proof.