@janneke given how carefully it is made, i have to assume the guile makers know what they are doing (and i know them and know that they do), and don't doubt that there are good reasons. but i'm very used to nil punning like the blazes, i find it elegant. without it, when/unless become unusable to me.
i also don't see why we need three nonentities. can't your queries be satisfied with 2? calling (unspecified?) on something is a monstrosity.... why not return false for a failed when?
but anyway, guile v v good :), maybe one day i will see the light re holy prohibition on nil punning!