Semantics of object assertions

[skuzzle]

Hey,

I'm trying to understand the semantics of std.prune with regard to assertions. Specifically I'm wondering why:

$ jsonnet -e "std.prune({assert false})"                                     
{ }

doesn't raise an exception.

Is this a bug or does it actually make sense? I don't think the specification describes in detail at which point object assertions are to be evaluated, that's why I'm asking.