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Re: Re: Incrementing a Global variable

Subject: Re: Re: Incrementing a Global variable
From: David Carlisle <davidc@xxxxxxxxx>
Date: Thu, 28 Aug 2003 13:39:28 +0100
kind of variable
> Would it not be nice if both kind of variables are
> available -- the present kind ( <xsl:variable ), and a
> second kind of variable (e.g. xsl:variable2 ) which
> can increment. It will be the programmer's
> responsibility to use xsl:variable (non-incrementable)
> or xsl:variable2(incrementable)..

That wouldn't be nice at all, it would totally change the
way XSLT works. XSLT templates may be evaluated in any order,
variable values may either be stored or re-calculated from the
expression on each use, code may be re-arranged and optimised
by the compiler. All of these things require that code is side effect

If you have a function f(x) and and expression

f(x) + f(x)

it may be optimised to 2 * f(x) which means you only have to calculate
the function once.

However you can't do that if there is a possibility of the "function"
doing something strange like incrementing teh value of some second
variable y as in the first case y goes up by 2 and in the second it goes
up by 1.

> If somebody wishes to produce a side-effect free
> program, he/she can use xsl:variable (which will
> facilitate that objective) ; if somebody wishes to use
> a incrementable variable , he/she can use the other
> one ..

Why use a functional language if you don't want to program in a
functional style. There are plenty of non functional languages to choose


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