Re: Side effects and large-scale conversion

Subject: Re: Side effects and large-scale conversion
From: Vivek Agrawala <vivek@xxxxxxxxxxxxxxx>
Date: Tue, 23 Sep 1997 11:02:02 -0400
Sam Hunting wrote:

> Has anyone ever used DSSSL for large-scale conversion (1000s of pages) --
> doubtful -- and if so, did the prohibition of side effects get in the way?
> Why or why not?
In the beginning, the prohibition of side-effects did get in my way.
Later, I found a way around it.

Some improvements in the area of passing information (state) down
the Flow Object Tree are coming, as discussed here a few months back.
Check the following threads in the DSSSL list archive:
 * On side-effects
 * DSSSL Design Question

> Why was the "no side effects" design decision made? Do I misunderstand
> that such a decision was made? If it has been made, is it a significant
> bar to doing "real programming" with DSSSL?

The design decision was made, and people closer to that discussion
will probably speak up.  But, approximately, the claim is that
prohibition of side-effects makes the development of DSSSL-based
intercative editors easier & more efficient.

> If so, where does one draw the line, especially given that DSSSL is
> extensible?

Yes, since it is extensible, one can provide side-effects via
external procedures.  The nice thing is that this leaves the
standard DSSSL side-effect free, while letting users with
special needs do what they want.
Of course, DSSSL specs written using these custom extensions
won't work with applications written for side-effect free
DSSSL specs.

-- Vivek Agrawala, Ph.D.
Siemens Corporate Research, Inc.	email: vivek@xxxxxxxxxxxxxxx

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