Cryptic C code?

[Doug Gwyn <gwyn>]

Well, yes, but.  Abstract objects (such as input data streams)
can have more than one interesting predicate.  What would
testing for the "truth" of such an object mean?  Clearly you
would have to include a (predicate) selection operation, and
that isn't notably different from just writing the boolean
expression (predicate) that one has in mind.  Just packaged
differently.