I wonder if it'd be worth aligning our F interface with JDK 8's in general, given that the latter is stable now. There probably wouldn't be much change.

At a minimum I think that anything new should copy the JDK 8 interface. In the case of Predicate:

http://download.java.net/jdk8/docs/api/java/util/function/Predicate.html

@jroper What'd think?