Re: On side effects

Subject: Re: On side effects
From: Paul Prescod <papresco@xxxxxxxxxxxxxxxxxxxxxxxxx>
Date: Tue, 17 Jun 1997 10:47:44 -0400 (EDT)
> There is however one thing that makes me suspicious and that is the side
> effect freeness of DSSSL. My experience is that for a real working progra=
> mming
> language you want and need side effects. Being free from side effects mak=
> es
> the languange hard to use in an application although it forces a good=20
> programming style. Maybe I am wrong and there may be several good reasons
> for this side effect freeness.=20

DSSSL is first and foremost a stylesheet language -- it just has a programming
language embedded within it. One of the important goals for a stylesheet 
language is usage in interactive applicatons like web browsers and word
processors. As long as processing something at the top of a document can't
affect processing at the bottom, then it is possible to render the thing at
the bottom without even looking at the thing at the top. This allows a user
to, for instance, jump to the bottom of a 10 MB file without waiting half
an hour for the first 9.9MB to be processed.

It is true that side effects are convenient for doing real programming. I
think that the right way to achieve this is to integrate the DSSSL flow 
objects and query language into more traditional languages. If you don't care
about WYSIWYG word processors or browsers then all you really want from DSSSL
is the standardized API to formatters and grove engines. Why not just embed
those APIs in your favourite programming language?

 Paul Prescod


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