Re: [Chicken-users] define-struct and equality

[Zbigniew]

Carlos,

'point' is represented internally as a 3-element vector, tagged as a
structure type.  Slot (element) 0 is the symbol 'point.  Slots 1 and 2
are for the x and y values, respectively.  You can therefore use
equal? to compare two records.  equal? also compares the slots
recursively as expected, so

(equal? (make-point (make-point 1 2) (make-point 3 4))
       (make-point (make-point 1 2) (make-point 3 4)))
; => #t.

On 6/24/07, Carlos Pita <address@hidden> wrote:
> Hi all,
>
> is there any warranty regarding equality and records? Experimentally I got:
>
> #;62> (define-record point x y)
> #;63> (define p1 (make-point 1 1))
> #;64> (define p2 (make-point 1 1))
> #;65> (equal? p1 p2)
> #t
> #;66> (eq? p1 p2)
> #f
> #;68> (eqv? p1 p2)
> #f
>
> So by-value equality seems to work between different record instances with
> equal field values, but I'm not sure that I can infer that from this
> example.
> Should I define my own equality predicate?
>
> Thank you in advance
> Cheers,
> Carlos
>
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