> 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.  

This example from Wikipedia shows that side-effects are harmful not only
in functional languages but also in imperative ones:

http://en.wikipedia.org/wiki/Side-effect_(computer_science)


> Beyond provability and state reliability, are
> there any other challenges?   A better understanding of the danger
> allows for an improved assessment of risk.

Nobody here even bothers about provability. Stated in a general form,
using functions with side effects in a uncontrolled manner leads to
unpredictable results, which can change from one language processor to
another or from one version of a language processor to another or even
from one run of the program to another run with the same language
processor.

Examples are available.

Dimitre Novatchev.
FXSL developer,

http://fxsl.sourceforge.net/ -- the home of FXSL
Resume: http://fxsl.sf.net/DNovatchev/Resume/Res.html





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