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setcar
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(setq x '(1 2)) ⇒ (1 2)
(setcar x 4) ⇒ 4
x ⇒ (4 2)
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(setq x1 '(a b c))
⇒ (a b c)
(setq x2 (cons 'z (cdr x1)))
⇒ (z b c)
;; ¶¦ÍÉôʬ¤ÎCAR¤òÃÖ¤´¹¤¨¤ë (setcar (cdr x1) 'foo) ⇒ foo x1 ; ξÊý¤Î¥ê¥¹¥È¤¬Êѹ¹¤µ¤ì¤Æ¤¤¤ë ⇒ (a foo c) x2 ⇒ (z foo c)
;; Èó¶¦ÍÉôʬ¤ÎCAR¤òÃÖ¤´¹¤¨¤ë (setcar x1 'baz) ⇒ baz x1 ; 1¤Ä¤Î¥ê¥¹¥È¤À¤±¤¬Êѹ¹¤µ¤ì¤Æ¤¤¤ë ⇒ (baz foo c) x2 ⇒ (z foo c)
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b
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--- --- --- --- --- --- x1---> | | |----> | | |--> | | |--> nil --- --- --- --- --- --- | --> | | | | | | --> a | --> b --> c | --- --- | x2--> | | |-- --- --- | | --> z
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x1: -------------- -------------- -------------- | car | cdr | | car | cdr | | car | cdr | | a | o------->| b | o------->| c | nil | | | | -->| | | | | | -------------- | -------------- -------------- | x2: | -------------- | | car | cdr | | | z | o---- | | | --------------