[REBOL] Re: ticket #6863

From: lmecir::mbox::vol::cz at: 24-Jul-2001 5:50

Hi,

> This approach has one major problem.  Your mut-equal? function has the
> side effect that is may cause a re-allocation for the series because
> it adds a value to it.
>

You are right. This version tries to modify the series only in "special
cases",
while getting the correct result:

    indexz?: function [
        series [series!]
    ] [orig-tail result] [
        orig-tail: tail :series
        while [
            error? try [result: (index? :series) - 1]
        ] [
            if empty? head :series [
                append :series #"1"
            ]
            append :series head :series
        ]
        clear :orig-tail
        result
    ]

    mut-equal?: func [
        {
            a discernibility test,
            useful to discern SERIES! values
        }
        a [series!]
        b [series!]
    ] [
        found? all [
            same? tail :a tail :b
            equal? indexz? :a indexz? :b
        ]
    ]

    a: [1]
    insert a reduce [a]
    b: [1]
    insert b reduce [b]
    mut-equal? a a/1 ; == true
    mut-equal? b b/1 ; == true
    mut-equal? a b ; == false
    a: [1]
    b: tail a
    remove a
    mut-equal? b b ; == true

Trying to use the SAME? function instead of the MUT-EQUAL? function reveals
the bugs of SAME?.

Regards
    Ladislav

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