CLHS: Section 3.4.1.6

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## 3.4.1.6 Examples of Ordinary Lambda Lists

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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