should this give a compile error?

module santa
    implicit none
    interface
        module subroutine rudolph(nose)
        end subroutine rudolph
    end interface
end module santa

This compiles just fine by default options. If you set for warnings about undeclared variables you do get a warning. To my thinking (which may be wrong) the inheritance from the parent module should mean that rudolph's nose should have an explicit type in Santa's module.