Re: () eq () vs () = ()

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Subject: Re: () eq () vs () = ()
From: David Carlisle <davidc@xxxxxxxxx>
Date: Fri, 30 Sep 2011 12:00:36 +0100

On 30/09/2011 11:48, Andrew Welch wrote:

() = () returns false

deep-equals((),()) returns true

That's interesting, I'm guessing it has to be a 'just because'

it can be sort of justified

deep-equals tries to tell you if the sequences passed in as arguments are equal or not and () and () being the same are equal as sequences.

eq and = never consider the sequence as a whole, they only consider individual items

eq just considers single items and (because if sql heritage, probably, empty sequences) so returns () when given ().

= is an existential quantified comparison and the answer to
"is there an item in the first sequence equal to an item in the second"
is trivially false, since there are no items, so = returns false.

So, each operator (with the possible exception of eq, which would perhaps most naturally have been defined to be an error on () eq () ) has a natural justification, and so the user will never be confused and order is restored to the universe...

David


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Current Thread

() eq () vs () = ()
- Andrew Welch - 30 Sep 2011 09:43:50 -0000
  - Stefan Krause - 30 Sep 2011 09:54:26 -0000
    - Andrew Welch - 30 Sep 2011 10:48:17 -0000
      - David Carlisle - 30 Sep 2011 11:00:49 -0000 <=
      - Wendell Piez - 30 Sep 2011 15:16:08 -0000
      - Message not available
      - G. Ken Holman - 30 Sep 2011 11:03:12 -0000
      - Andrew Welch - 30 Sep 2011 11:28:30 -0000
      - Message not available
      - G. Ken Holman - 30 Sep 2011 12:26:43 -0000

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Re: () eq () vs () = (), Andrew Welch	Thread	Re: () eq () vs () = (), Wendell Piez
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