On 8/16/06, Charles Bailey wrote:
This is where the "eternal" part starts to confuse me (not picking on
your wording, but on the semantics).


I'll pick on the wording (wording should always be picked on -- not to be pedantic (OK, I like to be pedantic, but that's not the *only* reason!), but because it really is an advantage to develop terminology that's as precise and pretty as possible).

Maybe values can be considered "eternal", in some philosophical platonic sense, but variables certainly aren't (eventually your program will reach the end or the sun will explode or something). "Permanent", maybe...

What happens if I insert the C<$aa = "Two"> before line 255?  In other
words, can I rely on P6 to know at line 3 that there's an alias out
there by which C<$a> _might_ change without assignment later (i.e. the
guarantee that "$a and $b will remain the same unless you assign to
one" might be violated)?

...but there's nothing permanent either really, because you can always change any variable you like, later on at line 255. (Unless the variable is a constant, which is not the same thing as being immutable even though those words are fairly synonymous, i.e. yet more confusing terminology.)

What we're really talking about is action-at-a-distance: one variable changing its value because *something else* changed -- some other variable that was somehow "contained inside" the first one.

Not to be confused with changing some other variable that is really the same variable because they were bound together: $a:=$b. Should I call that two variables (somehow "linked" or bound together)? Or would it be better (easier, less confusing) to call it *one* variable that has two names? (Still nothing to be described as "permanent" here, because I can always unbind them later on, and have $a and $b being two completely separate variables, right?)

I find myself tempted to talk in temporal terms to explain the issue, and that's a natural way to frame examples, but the language of examples doesn't seem to be that good for explaining the concepts. Whether stuff may or may not change isn't the point; what it comes down to is referring to a variable itself vs. evaluating it.


-David

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