edit definition

[Moon@STONY-BROOK.SCRC.Symbolics.COM (David A. Moon)]

Try

    (defmacro deffoo (name)
      (let ((predicate (intern (format nil "~a-P" name))))
      `(sys:multiple-definition ,name deffoo
         (blah-blah-blah)
         (defun ,predicate (x)
           (typep x ',name))
         ',name)))

I must confess that I cannot understand why this remains undocumented.