equal? on arrays

equal? on arrays

[Kevin Ryde]

What can be said in the manual about `equal?' on arrays these days?
Can vectors and 1-dim arrays be compared with equal now?  Is it still
the case that all shared arrays have to be compared with
`array-equal?' ?


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Re: equal? on arrays

[Marius Vollmer]

Kevin Ryde <user42@zip.com.au> writes:

> What can be said in the manual about `equal?' on arrays these days?
> Can vectors and 1-dim arrays be compared with equal now?  Is it still
> the case that all shared arrays have to be compared with
> `array-equal?' ?

It should clearly be possible to use equal? with all kinds of arrays.
If this isn't the case, we would need to fix.  (I hope that the fix is
as easy as documenting the bug in this case...)

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Re: equal? on arrays

[Kevin Ryde]

Marius Vollmer <mvo@zagadka.de> writes:
>
> It should clearly be possible to use equal? with all kinds of arrays.
> If this isn't the case, we would need to fix.

Eg, picking out a diagonal with a shared array:

    (equal? (make-shared-array #2((a b c) (d e f) (g h i))
                               (lambda (i) (list i i))
                               '(0 2))
            #(a e i))
    => #f

but with array-equal? it's #t.

It was this way in guile 1.6 too, but never really documented under
equal?, unless you know or thought a shared array is not really an
array.


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Re: equal? on arrays

[Marius Vollmer]

Kevin Ryde <user42@zip.com.au> writes:

> Marius Vollmer <mvo@zagadka.de> writes:
>>
>> It should clearly be possible to use equal? with all kinds of arrays.
>> If this isn't the case, we would need to fix.
>
> Eg, picking out a diagonal with a shared array:
>
>     (equal? (make-shared-array #2((a b c) (d e f) (g h i))
>                                (lambda (i) (list i i))
>                                '(0 2))
>             #(a e i))
>     => #f
>
> but with array-equal? it's #t.
>
> It was this way in guile 1.6 too, but never really documented under
> equal?, unless you know or thought a shared array is not really an
> array.

The problem is that #(a e i) is a vector (scm_tc7_vector) while
make-shared-array returns a smob.

In Guile 1.6, you could not use vector-ref with a one-dimensional
array smob (but you could use array-ref with a vector).  Thus, you
could say that a one-dimensional array is not a vector and can not be
equal to it.  It also prints differently.

In Guile 1.8, you can use vector-ref with a one-dimensional array
smob, and they print identical.  Thus, they should be equal? now.

I'll fix this.

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