World: r3wp

FOUND? and TRUE? take time to execute, and often make it necessary 
to put code in parentheses, which also have overhead. Silly interpreted 
language stuff, but it's significant.

Actually, the case of TO-LOGIC, FOUND? and TRUE? shows what is bad 
about it. Does common user know which should be used?

They are not interchangeable!

(i don't really know.. never used true?.. looks a bit silly. i got 
used to the conditional meaning of stuff, so i hardly use AND/OR 
but ANY/ALL instead :)

I often use the prefix forms of AND, OR and XOR because of the parentheses 
issue. Operations used often, but not always the operators.

AND~, OR~ and XOR~ are the power-reboller's friend :)

A little comparison of TO-LOGIC, TRUE? and FOUND?:

>> to-logic 0
== false

>> true? 0
== true

>> found? 0
== true

>> to-logic false
== false

>> true? false
== false

>> found? false
== true

So, this state is not what could make an uninitiated user happy.

onetom ~/rebol $ grep -riw AND `find . -iname \*.r` | wc -l

i ran this for OR too and 95% of the occurances are in comments or 
strings and where it's found in the code, it's usually used as a 
bit-wise operator

(i have rebgui, cheyenne, vid-ext, rebdb, host-kit, musiclessonz, 
power-mezz, glass, r3 gui in this folder. ~500 files)

aha, fine, that is perfectly possible, but, it may be caused e.g. 
by the fact, that you actually are forced to use ANY and ALL for 
processing conditional values, since AND and OR are not working satisfactorily 
for that purpose

Ladislav: yes, probably that is the case; which for example i am 
completely happy with

I prefere ANY and ALL for this reason:

>> if (print 1 true) AND (print 2 false) AND (print 3 true) [print 
4]
1
2
3
== none

>> if all [(print 1 true) (print 2 false) (print 3 true)][print 4]
1
2
== none

It confused me a bit, what exactly was meant by "conditional AND 
and OR". So it's not just, that they operate on logic values, but 
that the second operand is only evaluated, if needed.

I presume, it'll be hard to implement conditional AND and OR in REBOL, 
because it's not just a type check as with other operators.

it's not just, that they operate on logic values, but that the second 
operand is only evaluated, if needed

 - actually, you missed the explanation. "Conditional" was coined 
 by Brian and was meant to represent functions able to yield values 
 usable as CONDITION arguments of IF etc. as well as being able to 
 combine conditional expressions into more complex conditional expressions 
 (which is not true for AND and OR as demonstrated)

no other property was mentioned

Aha, then we're back to my original understanding, and then I don't 
understand, why you say
REBOL does not have conditional AND and OR

REBOL does to some extend:

>> true and true
== true

Isn't that a conditional AND from your (or Brian's definition)?

no its a logical one.   it only compares logic!  datatypes correctly.

(within a conditiional minset)

true and 1
none or none

each operand could be a parameter for IF/EITHER/UNLESS and has it's 
very well defined logic! value

Yes, I understand, but wouldn't it possible confuse Carl to say "REBOL 
does not have conditional AND and OR". It does to some extend, right?

thats why i was asking for an explicite definition above

ok :)

I guess, there are several problems in this. Some conditions are 
dealt with by AND and OR, the logic! ones. But not all conditions, 
IF/EITHER/UNLESS can handle is supported by AND and OR. And second, 
AND evaluate all operands, even if some are false. That is the definition 
of "conditional AND and OR" I found from a search:

http://download.oracle.com/javase/tutorial/java/nutsandbolts/op2.html


See "The Conditional Operators" a bit down and the mention of "short-circuiting" 
behavior.

Not having the "short-circuiting" behaviour is a direct bug, as I 
see it. Because this code with create an error:

if (port <> none) and (data: read port) [ ... ]


But I have a gut feeling, that logic AND isn't very REBOLish, and 
that's why we more often use ALL and ANY. It's just a feeling, so 
feel free to disagree.

yeah, i had the same feeling that it can be interpreted as the description 
of a non-complete boolean evaluation  (that was the name of the flag 
in turbo pascal ;)

with -> will

the original problem was not AND/OR but NOT

so IF NOT is not the same as UNLESS

(if im correct)

or actually it is but then AND/OR why not

capable of handling the same parameters as NOT?

the basic problem is that NOT isn't symmetric with AND/OR/XOR .  
  currenty, AND/OR/XOR are bitwise ops.  they are not language control 
flow ops.

it raises the question, well what are these ops... and the answer 
is that there are none.   its a strange hole in the language spec 
which has passed under the radar for a really long time.

its very possible that REBOLers think in a different way and using 
ANY/ALL is more natural, hence the unatention this has had.

I don't agree, they're only used bitwise, as this example illustrate:

>> a: 1 b: 2
== 2
>> if (a = 1) and (b = 2) [print "it's true"]
it's true

Geomol: I don't understand, why you say
REBOL does not have conditional AND and OR


Excerpt form the above definition of "conditional operator": "...being 
able to combine conditional expressions into more complex conditional 
expressions..."


The demonstration that AND and OR are not able to combine conditional 
expressions into more complex conditional expressions is easy

(and has been done already)

I just got confused by the wording. :-)

Is it correct to say, that AND and OR can be used as bitwise operators 
and to check on logic! values. And that e.g. IF can do more than 
this and then isn't really compatible with AND and OR?

geomol, logic types are single precision states.  on or off.  any 
operation between logic values are implicitly bitwise.

yep.

you just got the differentiation between conditional and logical 
comparisons.

Ah yes, you can say that about bitwise. Makes sense.

I'm just used to not think in bits when dealing with logics.

I am trying to use a slightly different formulation: IF can check 
not just logical expressions (yielding LOGIC! values), but conditional 
expressions (yielding any values). We do not have operators combining 
conditional expressions into more complex conditional expressions 
(ANY and ALL are dialects, not operators, although they can be used 
successfully).

Sounds good to me.

geomol,  I come from electronics background wrt logic... so I can't 
make the difference  ;-)   I studied logic as digital circuits vs. 
 analog circuits.