定义Lisp宏时，双引号(双逗号)有用法吗？

Is there a use for double unquote (double comma) when defining a Lisp macro?

当定义一个使用宏的宏或定义一个定义宏的宏时，似乎使用,',或,取消引用。我是否需要使用,,？

好的。

这是Graham的" On Lisp "中的代码：

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(defmacro =defun (name parms &body body)
(let ((f (intern (concatenate 'string
"=" (symbol-name name)))))
`(progn
(defmacro ,name ,parms
`(,',f *cont* ,,@parms))
(defun ,f (*cont* ,@parms) ,@body))))

另一个示例来自clx/gcontext.lisp：

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(macrolet ((def-gc-internals (name &rest extras)
(let ((macros nil)
(indexes nil)
(masks nil)
(index 0))
(dolist (name *gcontext-components*)
(push `(defmacro ,(xintern 'gcontext-internal- name) (state)
`(svref ,state ,,index))
macros)
(setf (getf indexes name) index)
(push (ash 1 index) masks)
(incf index))
(dolist (extra extras)
(push `(defmacro ,(xintern 'gcontext-internal- (first extra)) (state)
`(svref ,state ,,index))
macros)
;; don't override already correct index entries
(unless (or (getf indexes (second extra)) (getf indexes (first extra)))
(setf (getf indexes (or (second extra) (first extra))) index))
(push (logior (ash 1 index)
(if (second extra)
(ash 1 (position (second extra) *gcontext-components*))
0))
masks)
(incf index))
`(within-definition (def-gc-internals ,name)
,@(nreverse macros)
(eval-when (:execute :compile-toplevel :load-toplevel)
(defparameter *gcontext-data-length* ,index)
(defparameter *gcontext-indexes* ',indexes)
(defparameter *gcontext-masks*
',(coerce (nreverse masks) 'simple-vector)))))))
(def-gc-internals ignore
(:clip :clip-mask) (:dash :dashes) (:font-obj :font) (:timestamp)))

简而言之，这不是很常见，但并非闻所未闻。