Common Lisp：在不使用 &rest 参数的情况下有效地处理提供的 p 参数

Question

假设我有这个功能

(defun bar (a &optional (b nil bp))
  (declare (ignore a b bp)) ; <-- replace it with (list a b bp)
                            ;     to check for correctness
  )
;; I want to preserve the value of bp here inside bar, and inside foo below

我希望围绕bar写一个包装器：

(defun foo (a &optional (b nil bp))
  (declare (optimize speed))
  (apply #'bar a (nconc (when bp (list b)))))

同时在从foo 到bar 的调用中保留bp 的值，同时保持参数b 在emacs 的迷你缓冲区/eldoc 模式中可见。我想知道是否有一种可能不可移植的非 consing 方法来在此调用中保留 bp 的值。

例如，

CL-USER> (time (loop repeat 1000000 do (foo 4 2)))
Evaluation took:
  0.040 seconds of real time
  0.043656 seconds of total run time (0.043656 user, 0.000000 system)
  110.00% CPU
  96,380,086 processor cycles
  15,990,784 bytes consed <--- plenty of consing
  
NIL

如果我忽略 b-visibility-in-eldoc，我可能会使用 &rest 参数，但我确实希望参数可见。

虽然在这种特殊情况下还有其他方法可以实现这一点，但我确实想考虑存在多个 &optional（或 &keyword）参数的情况。

Answer 1

使用cond 表单来决定如何调用bar：

(defun bar (a &optional (b nil bp) (c nil cp))
  (declare (ignore a b bp c cp)))

(defun foo (a &optional (b nil bp) (c nil cp))
  (declare (optimize speed))
  (cond (cp (funcall #'bar a b c))
        (bp (funcall #'bar a b))
        (t (funcall #'bar a))))

CL-USER> (time (loop repeat 1000000 do (foo 1 2 3)))
Evaluation took:
  0.015 seconds of real time
  0.017203 seconds of total run time (0.017148 user, 0.000055 system)
  113.33% CPU
  41,186,554 processor cycles
  0 bytes consed

检查传递给bar的参数：

(defun bar (a &optional (b nil bp) (c nil cp))
  (list a b bp c cp))

CL-USER> (foo 1 2 3)
(1 2 T 3 T)
CL-USER> (foo 1 2)
(1 2 T NIL NIL)
CL-USER> (foo 1)
(1 NIL NIL NIL NIL)

Answer 2

我不确定 bar 和 foo 实际上应该做什么，但是：

(defun foo (a &optional (b nil bp))
  (declare (optimize speed))
  (funcall #'bar a (when bp b))) 

CL-USER> (time (loop repeat 1000000 do (foo 4 2)))
Evaluation took:
  0.005 seconds of real time
  0.005810 seconds of total run time (0.005804 user, 0.000006 system)
  120.00% CPU
  8,099,624 processor cycles
  0 bytes consed