Thanks - that sounds useful.
In the meantime, before that is available, would it be possible to include some calls to Task.checkCancellation() during the evaluation of the match? The use case I'm thinking of for this for evaluating a user-specified Regex in an interactive application. If the match operation is taking too long, it should be possible for the user to cancel this.
From SE-0304:
Functions which perform a large amount of synchronous computation may wish to periodically check for cancellation explicitly.