T/F var expansion?

[L A Walsh]

Is there a T/F var expansion that does:
 
    var=${tst:+$yes}${tst:-$no}

but with yes/no in 1 expansion?

Something like:

    var=${tst:^yes^no}
              |   |
              \___\___ or some other char(s)

    with the opposite syntax being allowed as

    var=${!tst:^no^yes}

(or) if '!' before the varname is unwieldy:

     var=${tst:!no!yes}

----
Obviously the 1 code-snippet solves the problem, but looks
a bit redundant, at the least...

Sorry if this is already implemented in some form, I'm just
not remembering there being one.