Failing faster: overlapping patterns for property-based testing

In property-based testing, a key problem is generating input data that satisfies the precondition of a property. One approach is to attempt to do so automatically, from the definition of the precondition itself. This idea has been realised using the technique of needed narrowing, as in the Lazy SmallCheck system, however in practice this method often leads to excessive backtracking resulting in poor efficiency. To reduce the amount of backtracking, we develop an extension to needed narrowing that allows preconditions to fail faster based on the use of overlapping patterns. We formalise our extension, show how it can be implemented, and demonstrate that it improves efficiency in many cases