Re: The real harm is in functions with side effects (W

----- Original Message ----- 
From: "Dimitre Novatchev" <dnovatchev@xxxxxxxxx>
>
> "Joshua Allen" <joshuaa@xxxxxxxxxxxxx> wrote in message
>
news:0E36FD96D96FCA4AA8E8F2D199320E52BA807D@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > Well, doing so partially defeats the purpose of using XSLT, since it
> > means your stylesheets will not work in many other systems.  It begs
the
> > question, if you find that Java is needed, then why use XSL at all?
Why
> > not just write the app in Java?

If one is already working in an infrastructure supporting
transformations, an extension can take advantage of working with a
parsed object and established (and possibly memory resident) stylesheets
and write just the code required to supply what is wanted.

> Portability is not the main issue with using extension functions.
>

The portability of the message is the significance of XML.  The
portability of stylesheets is often a secondary concern.  Local
processing of the message is often dependent on local requirements.

> In many cases an application is designed to work only within a certain
known
> platform/environment (e.g. intranet), which is not going to change.

While *not going to change* is a forceful and often mistaken assumption,
there are obvious examples within a discrete application.  Outward
facing stylesheets prefer portability, inward facing ones, such as those
intended to improve data-hiding and encapsulation, usually have a
controlled execution environment.

> We need to have a special section in the XSLT FAQ about extension
functions
> and why functions with side effects are generally harmful in a
functional
> language.

Dimitre, could you refer us to a general discussion or monograph which
illustrates the problems for functional languages, not specific to XSLT.
I understand that the absence of side effects is a design goal for
functional languages.  Beyond provability and state reliability, are
there any other challenges?   A better understanding of the danger
allows for an improved assessment of risk.

Mike



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