glogla on Interviews Can Be a Terrible Way to Identify Good Programmers

Oh boy.

I seem to remember the

  (member 1 '(1 2 3)) -> t
  (equal '(1 2) '(1 2)) -> t
  (member '(1 2) '('(1 2) '(3 4))) -> nil

bug. It took me just three hours, but boy was it annoying. In the end, it was just me not knowing the language of course.

I can read just enough of that that it confuses me why it doesn't work. Care to explain?

The problem is, that

  (equal 1 1) -> t
  (equal '(1 2) '(1 2)) -> t

  (eq 1 1) -> t
  (eq '(1 2) '(1 2)) -> nil

because eq tests for the same symbol, while equal test for the same list. Member uses eq, not equal.

If we are talking Common Lisp, the default test is actually EQL. ((eq 1 1) is not necessarily T).

Ah, I see. Thanks.

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