[REBOL] Re: On mutability and sameness
From: joel:neely:fedex at: 16-Jun-2001 23:30
Hi, again, Ken,
Using the ideas in my reply to your previous post (I just
sent it a couple of minutes ago)...
Ken Anthony wrote:
> ...and how about this?
>
> a: [1:30]
> b: [1:30]
> same? a b ;==false
>
...this outcome is easy to predict. Notice that A and B
are both blocks, with EQUAL? content, but since they were
constructed separately, they are not the SAME? block.
> same? do a do b ;==true
>
Remember that when DO is given a block, it evaluates all
expressions in the block, and returns the value of the last
expression as its result. Given that fact:
>> do a == 1:30
>> do b == 1:30
>> same? do a do b == true
The result value from DO A is the TIME! value of 1:30, and
likewise for DO B . Since TIME! is not a reference type,
any occurrence of 1:30 is the same as any other occurrence
of 1:30. Therefore, any expression that produces a TIME!
value of 1:30 yields a result that is SAME? to the result of
any other expression yielding 1:30, even something like:
>> 0:30 * 3 == 1:30
>> same? do a 0:30 * 3 == true
>> same? 2:00 - 0:30 0:30 * 3 == true
-jn-
------------------------------------------------------------
Programming languages: compact, powerful, simple ...
Pick any two!
joel'dot'neely'at'fedex'dot'com
