Macro expansion: Why doesn't the invoked macro see (let (variables)) from the invoking one?

[Alan Mackenzie]

Hello, Emacs.

One macro FOO binds a let variable, then invokes another macro BAR.  BAR
doesn't see this let variable.  Why not?  Is there anything I can do
about this?

(defmacro BAR ()
  (message (if (boundp 'asdf) "asdf" "no asdf"))
  '(message "bar"))

(defmacro FOO ()
  (let (asdf)
    `(BAR)))

-- 
Alan Mackenzie (Nuremberg, Germany).