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What is the difference between '(abc) and (list' a 'b' c)?

I read "On lisp" and ran into this code (I simplified it a bit).

CL-USER> (defun foo () '(abc)) FOO CL-USER> (foo) (ABC) CL-USER> (nconc * '(DE)) (ABCDE) CL-USER> (foo) (ABCDE) CL-USER> (defun foo () (list 'a 'b 'c)) STYLE-WARNING: redefining FOO in DEFUN FOO CL-USER> (foo) (ABC) CL-USER> (nconc * '(DE)) (ABCDE) CL-USER> (foo) (ABC)

  • What does * mean? Is this a previous function call? Can I use code in the real world?

  • Why (nconc * '(DE)) change the return value of the first function foo ?

  • I always thought that (list 'a 'b 'c) and '(abc) match? What is the difference?

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2 answers

When LIST is called, a new list is created each time it is computed. A list literal can be placed in a read-only memory segment after compilation. Destructive updating in lists using NCONC is then problematic, possibly with undefined consequences (segmentation error, literal change for future links or nothing at all).

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The variables * , ** and *** are indicated by the standard language, and they are very useful when testing things. They are a feature of REPL, and therefore they should not and should not be useful in "real-world code."

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