Re: New XT release

[Guy_Murphy@xxxxxxxxxx]

I thought the same way as Paul.

The 400 years of maths is all very interesting, and I do understand the
point that imperitive languages may well have got it wrong ::shrug:: IT
terminology is how it is however, and I don't see any needs being met over
here by cutting across the grain of such terminology because the
traditional usage in pure maths.

A constant is a label assigned a value that doesn't change after
assignement, a variable is an assignment to a label that can be changed. I
think most people comming to XSL will be expecting this usage of
terminology whether they be misguided or otherwise.

Cheers
     Guy.





xsl-list@xxxxxxxxxxxxxxxx on 04/21/99 04:47:44 PM

To:   xsl-list@xxxxxxxxxxxxxxxx
cc:    (bcc: Guy Murphy/UK/MAID)
Subject:  Re: New XT release



[SNIP]
Since reading Frank's comments, I agree with his reasoning and now better
understand the specification writers' use of the term.
I hope this helps.
........ Ken

From: "Frank A. Christoph" <christo@xxxxxxxxxxxxxxxxxx>
To: <dssslist@xxxxxxxxxxxxxxxx>
Subject: Re: Global variable
Date: Tue, 2 Mar 1999 12:20:38 +0900
[SNIP]
I can't resist replying to your appalling suggestion that "variable" is a
misnomer here. This contradicts at least 400 years of a mathematical
practice. If anything, it is the use of the word "variable" in imperative
programming languages like C that is misleading (not because C variables
aren't variables, but because they are much more sophisticated than plain
old everyday variables).
A variable in the mathematical sense most certainly _does_ vary; it varies
over its domain of values. It is the _denotation_ of such a variable that
does not vary, i.e., its meaning, what it refers to. If I write, for
example,
(define x 6)
then I am saying that 1) x is a DSSSL variable, and hence it varies over
the set of DSSSL values, and 2) its _value_ happens to be the constant, 6.
The fact that x is a variable, not a constant, is evident from the
semantics of DSSSL expressions, which dictate that I can substitute the
value of x for any occurrence of x without changing the meaning of
enclosing expressions (well, not really, but for the most part this is
true). The definition above expresses the fact that x = 6; consequently,
for any expression E in the scope of this definition, I can substitute 6
for x in E, written E[6/x], and be assured that E = E[6/x] because x = 6.
For example, (+ x x)[6/x] = (+ 6 6) follows from x = 6 which follows from
(define x 6) being in (the nearest) scope. More generally, this is known as
Leibniz's law of substitution of equals (for equals).
--FC


--
G. Ken Holman                  mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
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