World: r3wp

This page suggests that the "internals" of R3 does have NaN defined 
http://www.rebol.net/wiki/Decimals-64but it doesn't appear to be 
accessible.

Related topic, Jerry: INFs (see comment from Carl, which perhaps 
offers some hope that the situation will be normalised one day):
    http://www.curecode.org/rebol3/ticket.rsp?id=1717

This page suggests that the 

internals" of R3 does have NaN defined" - how does the text suggest 
it? I, as a coauthor will try to correct the text, if it does.

Certainly, IEEE754 defines NaN, but Rebol does not need to use/define 
it in any way.

So, for Rebol decimals, NaN is not defined/supported at present, 
nor are there any plans to use it in the future.

Thanks for the answer, Ladislave.

(but, of course, if such a wish exists, there is always the possibility 
to put it as a wish to CureCode)

yes, put it in curecode. if it's rejected, at least there would be 
documentation of why it's rejected.

Do we know a reason why it is desirable to have decimal! NaNs?

Ladislav - The following sentence implies that there is an internal 
NaN:
 

The exponent value 2047 is reserved for overflow and NaN (Not a Number)

I wrote that, I think. I got it from a IEEE 754 definition, like
http://en.wikipedia.org/wiki/IEEE_754-1985

Think of that part of the text as a description of the floating point 
standard used by CPUs.

Maybe you can try
to-decimal #{ ... 16 digits ... }

If that still works, you can use it to test, what you get, when you 
construct numbers like NaNs. To see how REBOL3 handle it.

Just checked. That sentence is in the section named "IEEE754 standard", 
so it is OK.

The IEEE754 standard reserves such a value for NaNs, overflow, etc. 
But, that does not mean, Rebol has to implement those.

BTW, "reserved for X" does not mean "X is implemented", it just means, 
that it should not be used for other purposes.

Nevertheless, I would like to see some coherent reasons why to support 
NaNs in Rebol.

As far as I am concerned, I guess, that Carl felt that:

>> 1 + (square-root -1) / 2
** Math error: positive number required
** Where: square-root
** Near: square-root -1

is more comfortable, than

>> 1 + (square-root -1) / 2
== #[NaN]

could be

The primary reason for supporting NaNs would be for easy of interaction 
with systems that do support NaN, eg Oracle.


Right now, any REBOL system that was trying to trade values with 
an Oracle system that supported NaN and +/-INF would need to code 
for special cases.


However, I do not know of anyone who has such a need -- so time for 
some to make the busines case!

Business case for NaNs???? Zero probability.

It depends on the business :)

I am sure, that my estimate is accurate

perhaps it's better to look at why other languages implement NaN.

Any particular language you do want to imitate?

If it's part of a standard, then I guess not. I'm guessing that languages 
like javascript implement it to make error handling of bad numbers 
easier in ways that may not be necessary for REBOL.

IIRC, the NaN stuff is mostly necessary in assembler and on the hardware 
level to trigger an exception and somehow report back a problem. 
If any layer now handles this exception it's not necessary to further 
bubble it upwards to interpreters, user scripts etc.

IMO In JS the NaN stuff is just annoying 'feature' which makes debugging 
harder.  Would you like to deal with the NaN or better just get an 
immediate error?

Many languages are implemented using C. If you don't do anything 
particular regarding NaNs, you get outputs like from this C program:

#include <math.h>
#include <stdio.h>

int main()
{
	printf ("%lf\n", sqrt (1.0));
	printf ("%lf\n", sqrt (-1.0));
	printf ("%lf\n", sqrt (2.0));
}

Output:

1.000000
nan
1.414214


So it may actually take more effort to grab the NaN output and make 
e.g. an error output. Like REBOL does:

>> square-root -1
** Math Error: Positive number required
** Near: square-root -1

(By REBOL example is by using R2. Not sure how R3 does this.)

*My*

I've never felt a need for NaN, but I also haven't done symbolic 
stuff or things where I think it would help to have it as a missing 
value. I'm open to it if there's a valid case though.

Pharo Smalltalk implements two methods as    isNaN    but has no 
such class  and  I no longer see NotANumber in Cincom Visual Works 
Smalltalk so that covers a new Smalltalk implementation ( Pharo )and 
a very mature implementation ( VW ).  Two recent languages to check: 
might be Falcon and Io ( falcon is not yet 1.0 at falconpl.org )

Re: "I am open to it" - maybe I misunderstood: do you mean, that 
you really want to obtain NaNs from expressions instead of errors 
being triggered?

guys, 2010 is almost finished, and R3 is still not there ;-( ....................but 
happy new year  anyway .................

Hope 2011 will bring us GUI; SQLite, REBDB and other databases connection; 
many tickets closed. I don't ask for more.

I hope Carl re-appears refreshed, and defines the beta-list. I wish 
for device extensions, user types,  tasking, timers, new codec system, 
network schemes :-)

Some of things might be done by the community, but some of those 
things are doable only by Carl ...

Pekr, too many things together. See you at the beginning of 2013 
:-)

Carl will probably reappear frustrated, because he's working on R2 
now ;-)

Ladislav, I meant that I'm fine with the current model, but if someone 
presents a strong argument for it I won't discount it out of hand.

What does WAIT NONE do?

It waits for events.

Ports implicitly waited for by WAIT NONE can be seen in the wait-list:
	print mold system/ports/wait-list

Check
	?? do-events

WAIT [ ] === WAIT NONE

13-Sep-2006 Anton Rolls

WAIT without also waiting for events:

view layout [
	button "wait 2" [
		remove find system/ports/wait-list system/view/event-port 
		
		wait 2 ; wait two seconds
		
		insert system/ports/wait-list system/view/event-port
	]
]

Oops, this is Rebol3 group. Sorry, I'm in Rebol2 head-space.

Thanks

I was hoping it would do more or less what you programmed: servicing 
system events but without waiting for all windows to close

How works the preallocation in R3? str: make string! 10000 length? 
str -> 0 dtto for blocks etc? why it happens in r3 program? prepared 
for future use?

Preallocation allocates the space needed to store the required number 
of characters into string. Nevertheless, the length of the string 
is zero, since the string initially does not contain any characters.

it's there primarily to help the garbage collector.