World: r3wp

Thanks, Ladislav. Good examples!


The thing, I missed, was that REBOL has this extra internal data 
structure to hold symbols (words), I though, just the contexts was 
used for that. So comparing words (that are not bound to any context) 
are much faster than comparing strings in REBOL. I see different 
possibilities, depending on implementation. If a word is changed 
to the result from a hash calculation, then two different words might 
give the same result, right? It's unlikely, but it could happen. 
That's why map datastructures are combined with lists, when two different 
hash calculations give same result. The other possibility is, that 
words are changed to pointers pointing to their entry in the map 
(hash table). Do you know, what of the two, REBOL implement? In other 
words, could two different words be equal in REBOL?


About the strings, then it's possible to do kind of the same with 
hashing. Lua does that. If you have two different but identical strings 
(same string content) in Lua, they share the same memory area. Hashing 
is involved, and I guess, comparing string would be equal fast as 
comparing words, if REBOL did the same. (unless words are exchanged 
with the result from the hash calculation, but then two words might 
be equal)

After a little testing, it seems, words are changed to a hash result, 
and REBOL gives an error, if two different words give same result:

>> s: "abcdefghijklmn"

>> forever [if equal? a: to word! random s b: to word! random s [print 
[a b]]]
** Internal Error: No more global variable space

The error comes really fast.

Petr, Nightwish? :-)

Above test is in R2.

R3 keeps going and can't be stopped with <Esc>.

<Esc> + <Ctrl>-c seem to stop it.

Global variable space should be the special object holding global 
values in R2. That's not the symbol table, either

My guess is that it must do more useless binding than R3

You're right. to word! put it in system/words, I need to do to block!, 
I guess.

Maybe to-lit-word works

In R2:

s: "abcdefghijklmn"

forever [if equal? a: to block! random s b: to block! random s [print 
[a b]]]

rebol-console: line 2:  5658 Floating point exception./rebol --noviewtop

A crash. Interesting! :)

Indeed

to lit-words! also put it in system/words in R2.

That's probably one of the things optimised away in R3

It's such a shame it's stalled

I think, Carl will return soon and he will open source R3.

He must have a hard time doing that other job, but probably he will 
experience the bright side of the open collaboration too.

Im expecting him to realize that he can actually help the world effectively 
if he can unleash the power us, the long time fans of rebol.

Don't hold your breath

John, to keep your mind on the edge of the cliff, did you know about 
the global series table? :-)

Not sure, what's that?

Quite similar to the global symbols table, the existence of a global 
series table can be deduced, from the R3 extensions interface

A series value does not include an index. Only a reference does. 
So that's one indirection, from a value slot (with an index) to a 
series value

But there must be another indirection, from the series value to the 
actual storage location of its item slots, because the item storage 
can't be counted on to stay at the same memory address over garbage 
collection and callbacks or multitasking, but it must be deduced 
that the series value can be counted on to stay at the same memory 
address

So there must be a table of series descriptors apart from the actual 
series content

Maybe it doesn't really need to be a global table, but it seems very 
convenient for the garbage collector

No, haven't heard of that.

It wouldn't need to be a global table, it could be a heap space dedicated 
to series descriptors (a typed array in memory). Same purpose, more 
likely implementation. Precise collectors are often implemented with 
type-specific heap spaces, since it reduces fragmentation when you 
don't have a copying or compacting collector - REBOL's collector 
doesn't move values, supposedly. REBOL could get away with heap spaces 
for block data, string/binary data, and descriptors (maybe both object 
and series in the same heap space); there might be more, but adding 
more can make the memory management more complicated.

I'm not sure how that differs from my description

can't be counted on to stay at the same memory address over garbage 
collection

 - as far as I know this has never been demonstrated. The performance 
 characteristics of REBOL's garbage collection are more consistent 
 with mark-and-sweep, and there hasn't been any indication that it 
 compacts or copies. Series reallocation on expansion does copy though. 
 Plus, there is a bunch of indication that R3 isn't yet task-safe 
 and that callbacks can choke on shared data too. Aside from that, 
 your argument's good, and your conclusion more so.

Well, I wouldn't count on it, but indeed, what the extensions documentation 
specifies is that series can move when they are changed. It's all 
very vague, but if the collector doesn't compact as you say, it would 
be restricted to expanding series beyond the internally allocated 
memory region

time-block? u mean delta-time?
 I mean TIME-BLOCK:

http://www.fm.tul.cz/~ladislav/rebol/timblk.r

could two different words be equal in REBOL?
 - in my opinion, that would be a bug

(unless intended, using aliasing)

heap spaces for block data, string/binary data,

 - there is absolutely no reason to have different spaces for strings 
 and blocks

aha, maybe there is

If you allocate strings only in multiples of 128 bits and aligned 
the same as blocks, fragmentation wouldn't be a problem if they are 
allocated in the same space. It would be a waste of resources for 
strings though, as even a single-char string would take 16 bytes 
of space.

Some memory management systems segregate the values by the size, 
with objects of similar sizes allocated from the same space, to cut 
down on fragmentation. Large enough objects are sometimes allocated 
on their own, in a seperate chunk of memory allocated from the OS. 
I haven't seen any indications that REBOL's memory management does 
this though.

Why does SKIP accept LOGIC! and PAIR! as its OFFSET parameter? Thanks.

pair! is for images, I think.

I have the same guess. Geomol

About logic, I guess, it's related to a wish to use PICK with logic 
argument. It works like this for SKIP:

>> skip [a b] true
== [a b]
>> skip [a b] false
== [b]

and you can use PICK instead of EITHER sometimes like:

value: pick [1 2] b > 1

instead of

value: either b > 1 [1] [2]

SKIP with TRUE as its 2nd argument, which made me think it DID skip. 
SKIP with FALSE as its 2nd argument, which made me think it DIDN'T 
skip. With your PICK example, now I understand.

Yes, the initial imagined behaviour is turned around with logic. 
:) The PICK method is also faster than the EITHER method, if it's 
simple values to pick. If you have to reduce the block, the EITHER 
method is faster, as EITHER already reduce its blocks.

In R2, you can pick from functions, like:

>> pick :to-integer 1
== [value]

and it works with true too, but not with false:

>> pick :to-integer true 
== [value]
>> pick :to-integer false
** Script Error: Out of range or past end

In R3, you can't pick functions like this.

SKIP with LOGIC value seems reverse,  because it doesn't convert 
logic to integer before use it:
>> to-integer true
== 1

See Core group!

Yep, I saw it.

LENGTH? 'WORD is 4, LENGTH? /WORD is 5 ... not 4. Why? is the heading 
#"/" in refinement counted?

I guess it counts / as part of it:
>> to-string /WORD
== "/WORD"

>> to-string 'WORD
== "WORD"

But I don't know if it is a bug or not.

To be able to type a word of datatype word!, we need lit-word!. Else 
the word would be evaluated to it's value. So when you write
	length? 'word
, it's the same as
	length? first [word]
To get what you want:
	length? first ['word]
or
	length? quote 'word