side-effect-free (was Re: Can solve the N-queens - but can't count!)

["James Tauber" <jtauber@xxxxxxxxxxx>]

>I think it would be useful to the debate if someone could articulate the
>reasons why stylesheets should be side-effect-free.

I won't claim to fully understand the implications of a stylesheet language
being side-effect-free, but a property that occurred to me this morning
while working on a little tool to help document XSL stylesheets was the
following...

Consider a template:

<xsl:template match="A">
    <xsl:apply-templates select="B"/>
    <xsl:apply-templates select="C"/>
</xsl:template>

As I understand, the side-effect-freeness of XSL means that when processing
this above template, you can go and apply the template for C before the
template for B, or run both in parallel, etc without having to worry that
something that applying one template does will affect the application of the
other.

JamesT


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