Ladislav:
> Rebol differs from human languages in some respects. One of them can be
found comparing Rebol Values vs. Human Values (see
http://www.geocities.com/lmecir.geo/evaluation.txt). This may be a surprise
for both experienced and inexperienced programmer, because that fact is
hidden in other programming languages to some extent. Another difference can
be found comparing the behaviour of Rebol (CQSB/DRP) functions with the
behaviour of their Pure CQSB counterparts (see
http://www.geocities.com/lmecir.geo/contexts.txt). A set of the differences
can be found studying the behaviour of code - modifying functions like
Repeat, Make Object!, Use, Foreach, ... The latter difference can be
considered a bug, of course, but it is present in Rebol nowadays.
This is quoted from Ladislav's web page:
<Quote>
; create a block Blk containing a word 'a
blk: copy [a]
a: 12
; now append another word to Blk
b: make object! [append blk 'a a: 13]
probe blk
; test if blk contains equal words
equal? first blk second blk
equal? get first blk get second blk
What is the reason behind such a "mystery"? The answer is simple:
*Words have Bindings*
and the first Word in Blk has a different Binding, than the second.
</Quote>
I differ slightly in my interpretation.
>> ; create a block Blk containing a word 'a
>> blk: copy [a]
== [a]
>> a: 12
== 12
>> ; now append another word to Blk
>> b: make object! [append blk 'a a: 13]
>> probe blk
[a a]
== [a a]
>> ; test if blk contains equal words
>> equal? first blk second blk
== true
>> equal? get first blk get second blk
== false
>> first blk
== a
>> second blk
== a
>> get first blk
== 12
>> get second blk
== 13
>> a
== 12
>> b/a
== 13
>> probe a
12
== 12
>> probe b
make object! [
a: 13
]
>>
Words have meanings (or values). The meaning of a word depends on it's
context. Two words may look the same, but can have different meanings,
because of their different contexts. 'b is an object with a different
context to the surrounding context. The word 'a inside 'b has a different
meaning from the 'a defined inside the global context. While the two words:
first blk
and:
second blk
look the same, they both result in 'a, they have different meanings. The
first means:
12
and the second means:
13
That's all there is to it. It's very like human language. For example,
"bear". There's a bear in the woods. That's all it can bear. Two words
exactly the same like [a a], but with different meanings. Here the
surrounding words supply the context, enabling the reader to know that the
first "bear" (a) means a four legged mammal (12), while the second "bear"
(a) means an amount of weight (13).
One can change the meaning of the word by binding it into a different
context. Here I bind the block into the global context:
>> bind blk 'a
== [a a]
>> get first blk
== 12
>> get second blk
== 12
and so make both words in the block mean the same. I can reassign the
meaning of the words in the block by 'bind-ing the block's words into the
context of the object 'blk, like this:
>> bind blk in b second first b
== [a a]
>> get first blk
== 13
>> get second blk
== 13
And I really like the simplicity of the line:
bind blk in b
which really means what it says. The only confusing thing is:
second first b
>> first b
== [self a]
'first on a object gets you a list of words in the object. While 'second
simply gets the first word after 'self:
>> second first b
== a
so allowing the 'bind to work.
>> help in
USAGE:
IN object word
DESCRIPTION:
Returns the word in the object's context.
IN is a native value.
ARGUMENTS:
object -- (Type: object)
word -- (Type: word)
Ladislav:
> My personal point of view is, that my previous experience with other
programming languages helped me to understand Rebol and appreciate its
advantages.
There's two succesful approaches to understanding Rebol. Have little
understanding of conventional computer languages - the innocent approach.
Have lots of understanding of conventional languages as Carl Sassenrath has
done and as most likely, Ladislav has. If you know one or a few conventional
third generation languages, then you're behind on the learning Rebol curve,
until you unlearn these languages.
Andrew Martin
See Rebol, Do Rebol, Know Rebol...
ICQ: 26227169
http://members.xoom.com/AndrewMartin/
-><-
