Re: [xsl] Scope of variables

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

At 04:46 AM 5/9/2003, David C wrote:
> When I first was shown programming (Fortran at school in the mid 70's)
> this aspect of fortran allowing variables to change their definition
> was the main "strange" thing about programming languages that all the
> books stressed. that programming languages had these strange imperative
> features because they were designed to be easily executed by machines
> rather than easily understood by humans.
>
> A generation later and things have changed: machines are now more
> powerful and so programming languages using more natural declarative
> constructs are now feasible. Let the machine do the work and have the
> language more suitable for humans. But things are not so simple, it
> seems that in the intervening time humans have got used to the
> imperative machine-oriented languages and are now unsettled by human
> oriented declarative languages. You can't win....

As a footnote to what David says, as a "human-oriented declarative 
language" XSLT seems to work best (partly; and I say "seem" because (a) 
this is actually a bit complicated, and (b) I just use these machines I 
don't build them) when you let it *manage for you* the processing logic of 
the operation (by letting it execute, where possible, a tree traversal). 
These are "templates", not "subroutines", and variables are mainly used to 
hold values that you may want and need, not control the process flow. Not 
long ago on this list I suggested an XSLT transform needs to be seen as an 
*output specification*, not a process. (At which someone helpfully 
mentioned the functional view: you are designing a function in terms of 
outputs for given inputs, and shouldn't have to worry about how the machine 
goes about executing it.)

It takes a real shift in mind set, especially when you run into problems 
for which XSLT *doesn't* give you direct support, and you find yourself 
implementing loops by recursion, etc. Not that that can't be done -- it 
can, and has been.

Cheers,
Wendell


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