Here are some examples involving optional parameters and rest parameters:
((lambda (a b) (+ a (* b 3))) 4 5) => 19 ((lambda (a &optional (b 2)) (+ a (* b 3))) 4 5) => 19 ((lambda (a &optional (b 2)) (+ a (* b 3))) 4) => 10 ((lambda (&optional (a 2 b) (c 3 d) &rest x) (list a b c d x))) => (2 NIL 3 NIL NIL) ((lambda (&optional (a 2 b) (c 3 d) &rest x) (list a b c d x)) 6) => (6 T 3 NIL NIL) ((lambda (&optional (a 2 b) (c 3 d) &rest x) (list a b c d x)) 6 3) => (6 T 3 T NIL) ((lambda (&optional (a 2 b) (c 3 d) &rest x) (list a b c d x)) 6 3 8) => (6 T 3 T (8)) ((lambda (&optional (a 2 b) (c 3 d) &rest x) (list a b c d x)) 6 3 8 9 10 11) => (6 t 3 t (8 9 10 11))
Here are some examples involving keyword parameters:
((lambda (a b &key c d) (list a b c d)) 1 2) => (1 2 NIL NIL) ((lambda (a b &key c d) (list a b c d)) 1 2 :c 6) => (1 2 6 NIL) ((lambda (a b &key c d) (list a b c d)) 1 2 :d 8) => (1 2 NIL 8) ((lambda (a b &key c d) (list a b c d)) 1 2 :c 6 :d 8) => (1 2 6 8) ((lambda (a b &key c d) (list a b c d)) 1 2 :d 8 :c 6) => (1 2 6 8) ((lambda (a b &key c d) (list a b c d)) :a 1 :d 8 :c 6) => (:a 1 6 8) ((lambda (a b &key c d) (list a b c d)) :a :b :c :d) => (:a :b :d NIL) ((lambda (a b &key ((:sea c)) d) (list a b c d)) 1 2 :sea 6) => (1 2 6 NIL) ((lambda (a b &key ((c c)) d) (list a b c d)) 1 2 'c 6) => (1 2 6 NIL)
Here are some examples involving optional parameters, rest parameters, and keyword parameters together:
((lambda (a &optional (b 3) &rest x &key c (d a))
(list a b c d x)) 1)
=> (1 3 NIL 1 ())
((lambda (a &optional (b 3) &rest x &key c (d a))
(list a b c d x)) 1 2)
=> (1 2 NIL 1 ())
((lambda (a &optional (b 3) &rest x &key c (d a))
(list a b c d x)) :c 7)
=> (:c 7 NIL :c ())
((lambda (a &optional (b 3) &rest x &key c (d a))
(list a b c d x)) 1 6 :c 7)
=> (1 6 7 1 (:c 7))
((lambda (a &optional (b 3) &rest x &key c (d a))
(list a b c d x)) 1 6 :d 8)
=> (1 6 NIL 8 (:d 8))
((lambda (a &optional (b 3) &rest x &key c (d a))
(list a b c d x)) 1 6 :d 8 :c 9 :d 10)
=> (1 6 9 8 (:d 8 :c 9 :d 10))
As an example of the use of &allow-other-keys and :allow-other-keys, consider a function that takes two named arguments of its own and also accepts additional named arguments to be passed to make-array:
(defun array-of-strings (str dims &rest named-pairs
&key (start 0) end &allow-other-keys)
(apply #'make-array dims
:initial-element (subseq str start end)
:allow-other-keys t
named-pairs))
This function takes a string and dimensioning information and returns an array of the specified dimensions, each of whose elements is the specified string. However, :start and :end named arguments may be used to specify that a substring of the given string should be used. In addition, the presence of &allow-other-keys in the lambda list indicates that the caller may supply additional named arguments; the rest parameter provides access to them. These additional named arguments are passed to make-array. The function make-array normally does not allow the named arguments :start and :end to be used, and an error should be signaled if such named arguments are supplied to make-array. However, the presence in the call to make-array of the named argument :allow-other-keys with a true value causes any extraneous named arguments, including :start and :end, to be acceptable and ignored.
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