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lambda-list-keywords

lambda-list-keywords Constant Variable

Constant Value:

a list, the elements of which are implementation-dependent, but which must contain at least the symbols &allow-other-keys, &aux, &body, &environment, &key, &optional, &rest, and &whole.

Description:

A list of all the lambda list keywords used in the implementation, including the additional ones used only by macro definition forms.

See Also:

defun, flet, defmacro, macrolet, Section 3.1.2 (The Evaluation Model)

Expanded Reference: lambda-list-keywords​

Inspecting the Value​

lambda-list-keywords is a list of all the lambda-list keywords recognized by the implementation. The standard requires at least the core keywords, but implementations may include additional ones.

;; Display all lambda-list keywords (implementation-dependent)
lambda-list-keywords
;; => (&ALLOW-OTHER-KEYS &AUX &BODY &ENVIRONMENT &KEY &OPTIONAL &REST &WHOLE)
;; (exact contents are implementation-dependent)

Required Keywords​

The Common Lisp standard mandates that certain keywords appear in this list. You can verify their presence.

;; Check for required keywords
(every (lambda (kw) (member kw lambda-list-keywords))
       '(&optional &rest &key &allow-other-keys &aux &body &whole &environment))
=> T

Using the List Programmatically​

lambda-list-keywords can be used by tools that parse or analyze lambda lists.

;; A simple function to separate parameters from lambda-list keywords
(defun split-lambda-list (lambda-list)
  (let ((params nil) (keywords nil))
    (dolist (item lambda-list)
      (if (member item lambda-list-keywords)
          (push item keywords)
          (push item params)))
    (values (nreverse params) (nreverse keywords))))

(split-lambda-list '(x y &optional z &key verbose))
=> (X Y Z VERBOSE)
=> (&OPTIONAL &KEY)