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google / lisp-koans

Common Lisp Koans is a language learning exercise in the same vein as the ruby koans, python koans and others. It is a port of the prior koans with some modifications to highlight lisp-specific features. Structured as ordered groups of broken unit tests, the project guides the learner progressively through many Common Lisp language features.

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Structure copying discrepancy?

drautb opened this issue · comments

commented

The last koan in structures.lisp talks about shallow copying at the end. It looks like this:

;; note that the copying is shallow
(let ((shallow-copy (copy-american-football-player manning-1)))
  (setf (car (nfl-guy-team manning-1)) "Giants")
  (assert-equal ___ (car (nfl-guy-team manning-1)))
  (assert-equal ___ (car (nfl-guy-team shallow-copy))))))

I expected the output the team for manning-1 to be "Giants", and the team for shallow-copy to be "Colts". However, the result is that they're both "Giants".

;; note that the copying is shallow
(let ((shallow-copy (copy-american-football-player manning-1)))
  (setf (car (nfl-guy-team manning-1)) "Giants")
  (assert-equal "Giants" (car (nfl-guy-team manning-1)))
  (assert-equal "Giants" (car (nfl-guy-team shallow-copy))))))

This looks more like deep copying, unless I'm misunderstanding something...

I'm using SBCL: SBCL 1.1.1.0.debian

commented

shallow copy means only copy the first level, not more.
(nfl-guy-team shallow-copy) point to (nfl-guy-team manning-1), so both are "Giants"

commented

As this issue has been answered/clarified and is apparently not bug-related, it seems like it could be closed, no?