[REBOL] Re: On mutability and sameness
From: joel:neely:fedex at: 17-Jun-2001 16:32
Hi, Ken,
Ken Anthony wrote:
> Joel, I'm being dense again.
>
> When you say the integers are immutable in Rebol (implying
> they may be mutable in other languages?)
>
Believe it or not, they used to be... ;-)
Questions 16-18 of "The Hacker Purity Test", found at
http://www.armory.com/tests/hacker.html
ask
16. 0x00F Ever change the value of 4?
17. 0x010 ... Unintentionally?
18. 0x011 ... In a language other than Fortran?
but that's a story for a long summer's evening in the
mountains with a campfire and some marshmallows.
> You referred to mutating verses replacing.
>
> > a: 42
> > a: a + 1 ;=43
>
> Could I not see this as an example of mutating the rightmost
> bit?
>
I don't think it's useful to do so. Suppose there had been
more intervening steps:
>> a: 42 == 42
>> b: a + 1 == 43
>> a: b == 43
or
>> a: 42 == 42
>> b: reduce [a + 1] == [43]
>> a: first b == 43
or even
>> a: 42 == 42
>> b: to-char a // 10 + 49 == #"3"
>> c: to-char (to-integer a / 10) + 48 == #"4"
>> d: rejoin [c b] == "43"
>> a: to-integer d == 43
Would that same idea still hold? At what point does "the 42"
get altered? I believe it's simpler to understand that
a: ... some expression ...
sets A to whatever the expression evaluates to, and it's only
coincidental that the expressions we've been talking about
happen to use the former value of A.
-jn-
------------------------------------------------------------
Programming languages: compact, powerful, simple ...
Pick any two!
joel'dot'neely'at'fedex'dot'com
