Variables and constants

[John Lam <jlam at iunknown dot com>]

This is more of a philosophical question. Since I haven't worked with
functional programming languages before, can anyone explain to me the
rationale for not having true variables a'la procedural programming
languages (i.e. you can re-assign the value of an existing variable)? 

Clearly this was an intentional design decision, but it makes it impossible
to do any kind of simplistic calculation (e.g. totalling a shopping cart
that has price and quantity information for each item) without resorting to
recursion. I feel that a lot of folks who will wind up using XSLT
(client-side DHTML developers in particular) will want to do things like
render a shopping cart for display *and* total the items in the shopping
cart without having to do the rendering transform using XSLT and the
totalling action by writing JavaScript code to walk the DOM.

Can anyone shed any light on why variables == constants in XSLT?

Cheers,
-John


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