proc
    islist(whatever)
        if(istype(whatever, /list))
            return TRUE

mob
    verb
        uhh()
            var
                i

            // Returns false.
            if(islist(i))
                world << "i is a list"

            var
                list/j

            // Returns false.
            if(islist(j))
                world << "j is a list"

            var
                list/k = list()

            // Returns true, this is a list!
            if(islist(k))
                world << "k is a list"