(define-modify-macro removef (item &rest remove-keywords)

  (lambda (seq item &rest keyword-arguments)

    (apply #'remove item seq keyword-arguments))

  "Modify-macro for REMOVE. Sets place designated by the first argument to

the result of calling REMOVE with ITEM, place, and the REMOVE-KEYWORDS.")

(define-modify-macro deletef (item &rest remove-keywords)

  (lambda (seq item &rest keyword-arguments)

    (apply #'delete item seq keyword-arguments))

  "Modify-macro for DELETE. Sets place designated by the first argument to

the result of calling DELETE with ITEM, place, and the REMOVE-KEYWORDS.")

It seems that the use of DEFINE-MODIFY-MACRO doesn't match the ANSI CL standard. HyperSpec[1] says the 3rd argument of DEFINE-MODIFY-MACRO must be a symbol, not a lambda expression. A new version of LispWorks (still under test) will cannot compile these two definitions: