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Re: Re: Incrementing a Global variable

Subject: Re: Re: Incrementing a Global variable
From: "Dimitre Novatchev" <dnovatchev@xxxxxxxxx>
Date: Thu, 28 Aug 2003 06:43:36 +0200
haskell global variable
"Mukul Gandhi" <mukulw3@xxxxxxxxx> wrote in message
> Hi Dimitre,
>   I am convinced that side effects are bad in a
> programming language.

I didn't say that... Waht I said is that uncontrolled side-effects are
dangerous. There are ways to control side effects reliably (e.g. using a
Monad Type Class) and these have been incorporated (supported at the
syntactic level) in some languages (e.g. the "do notation" in Haskell).

For explanation of Monads see:
Tackling the awkward squad: monadic input/output, concurrency, exceptions,
and foreign-language calls in Haskell, by Simon-Peyton Jones at:

This is also possible to implement in XSLT (and I have such an
implementation). Probably, in version 4 or 5 XSLT might have such a
mechanism incorporated into the language. A prerequisite for this is to make
functions first class objects (to treat them as any other data type -- to
allow functions to be passed as parameters and functions to be returned as
the result), which could happen in version 3 of XSLT.

One could always control side-effects manually, but this is tedious and

> Thanks for the links for
> information about this topic. I believe the objective
> of XSLT is to solve certain kind of problem(XML data
> transformations). The problem of generating serial nos
> comes frequently in real world situations.

This is not just one problem, but a class of problems. You haven't specified
which is exactly your problem. Many of these "serial number generation" or
"unique number generation" problems can be solved with a two-pass solution.

All of them can be solved by using recursive processing.

> Would it
> not be helpful(for transformations) if we can have a
> construct which can increment variables(not full scale
> -- but with limited features which can *aid* in
> transformations)?

If we have a robust mechanism for controlling side effects, then the answer
is yes.

> Are we not justifying functional
> nature of XSLT from a pure computer science view
> point..

No, this is not "science for the science" but just common sense derived on
very bad practical experience with side effects.

A programmer using an FP language must have understanding about the issue of
side effects, otherwise this would be like an 8 yr old driving a car.


Dimitre Novatchev.
http://fxsl.sourceforge.net/ -- the home of FXSL

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list

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