1. RE: 'Unknown' and three-valued logic (was: Example where Euphoria ...)
- Posted by rforno at tutopia.com
Nov 25, 2002
What you say about C is totally right. C does not check for pointers to
unexisting addresses, or addresses with random data; does not check for
uninitialized variables; does not verify validity of subindexes; does not
check for overflow; and has maybe some other flaws I am not recalling just
now.
But keep in mind that C was designed (not explicitly) as a replacement for
Assembly language, with the proviso that it can run under different
architectures.
Being an Assembly substitute, it has no place for nil data, the same as
Assembly. Machines work according to Boolean logic, which neither has place
for nil, only for True or False, or what is the same, 1 or 0.
The Euphoria language is another issue, and surely could have been designed
to work with some data type called "nil", but it has not. So, the only
solution I see to the problem is designing a package for it. But as I said
in a previous post, usual programming tasks do not need this facility, and
moreover, it is a pain in the neck to deal with tri-valued logic, as some
data bases allow.
Best wishes.
----- Original Message -----
From: Rom <kjehas at frisurf.no>
To: EUforum <EUforum at topica.com>
Sent: Sunday, November 24, 2002 3:30 PM
Subject: Re: 'Unknown' and three-valued logic (was: Example where Euphoria
...)
It is all C's fault.
I remember my first Toolswork C-compiler. It was absolutely a disasterous
experience for someone who's only experience was with Basic interpreters.
First the syntax errors.... then, if the program was not right, looose
pointers and that kind of things, causeing the program to go beserk and
easily crashed whole computer.
I am wondering how much C has shaped other programming languages, too? When
other languages are created using C, then the "*" operator are most likely
to be a C call? And the same goes for the relational operators ( =,>...) so
that the other languages created with C are likely to inherit the same
weaknesses as C? And C does not reserve any flag for a variable being
instanciated or not, it just uses whatever it find at that memory address,
there is no checking about the variable has been set or not (that is very
speedy ... which the designers of C wanted it to be).
So basicly, it the program is not right, then output will be rubbish
values... not nil values. When you tell a C program to multiply to variables
that are not set, then the result is rubbish... and there is no obvious way
to test if the values are rubbish or not.
When C evaluates a conditional statements upon a boolean value .... that is
not set ... then C branches in the wrong direction ...(and there is no
obvious way to test if current branch is caused by rubbish branchin)...
instead of branching in the direction it should have gone when branching is
unsolved.
It could all have been different... if there had been a nil flag for all
variables .. then all the compilers created with C would also have been
different ... because if C had been different, then the other compilers
would have inherited a lot of that behavior ... the best of it, hopefully?
It is all C's fault, behaving like an idiot.
Regards
Rom
==^^===============================================================
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2. RE: 'Unknown' and three-valued logic (was: Example where Euphoria ...)
- Posted by rforno at tutopia.com
Nov 26, 2002
----- Original Message -----
From: Rom <kjehas at frisurf.no>
Subject: Re: 'Unknown' and three-valued logic (was: Example where Euphoria
...)
From: <dm31 at uow.edu.au>
|C intially chose to represent a int by 16 bits, with first bit as
|sign-bit. They could have reserved one bit as nil-bit (nil-flag),
|meaning a int would have been in the range +/- 16384.
>And Programmers, like me, would not be very happy with our
> range oin each data type been halved for a flag that we would RARELY use.
Argument does not count because now we have 32-bits.
Argument counts, because you sometimes need to interface with other
programs/machines, and they have one more bit... This is the same with
Euphoria: EU integers ocasion some difficulties when interfacing C programs.
Do you have any "simple" solution for handling something as simple as an (A
and B and C) rule? (what people normally would regard as a rule)
(post Sent: Saturday, November 23, 2002 10:50 PM Subject: Unknown as a legal
var state?)
Rom
Example case: Simplified rules for unemployments benefits. How to program
such rules?
To qualify for unemployment benefits....
1) you must be a national citizen (N)
2) you must be unemployed (U)
3) you must have earned more than $10000 previous year (I)
4) all facts must be documented
==^^===============================================================
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3. RE: 'Unknown' and three-valued logic (was: Example where Euphoria ...)
- Posted by rforno at tutopia.com
Nov 26, 2002
The problem is not with the tools, but with the tri-valued logic itself.
Regards.
----- Original Message -----
From: Rom <kjehas at frisurf.no>
Subject: Re: 'Unknown' and three-valued logic (was: Example where Euphoria
...)
From: <rforno at tutopia.com>
> Being an Assembly substitute, it has no place for nil data, the same as
Assembly.
C intially chose to represent a int by 16 bits, with first bit as sign-bit.
They could have reserved one bit as nil-bit (nil-flag), meaning a int would
have been in the range +/- 16384.
> Machines work according to Boolean logic, which neither has place
> for nil, only for True or False, or what is the same, 1 or 0.
C could very well have implemented basic conditional statement as
if (a > 1) { ... }
ifnot { ......}
ifnil { .....}
Then if there was a nil on a flag on "a" then ifnil block would have been
executed.
ASM support this construction too ... just a matter of how to use ASM.
When is comes to pointers ... 0 is maybe nil-flag good enough.
Performing pointer checking all the way is maybe costly (thought ASM checks
eq 0 in a single instruction). Some basic changes here and we would have
OnError branching from the very start (I have never seen the C-code that
Euphoria produces ..... so I cannot say for sure that C's weaknesses will
be embedded in compiled Euphoria too?).
> So, the only solution I see to the problem is designing a package for it.
Ok, a global functions pNOT, pXOR, pAND, pOR can be defined in a couple of
hours:
eboolean a, b, c, decision
desicion = pAND( { a , b, c})
But constructs like
pAnd( a = False, b > 20 )
will not work ....there will be inconsistence between 3-valued boolean and
2-valued boolean.
eboolean A, B, C, D, decision --- 3-valued boolean
decision = affirm( A and B and (C or D) )
could maybe have been implemented in core ... maintaining full
backward.compatibily.
It cannot just be implemented as a library function.
> But as I said in a previous post, usual programming tasks do not need
> this facility, and moreover, it is a pain in the neck to deal with
tri-valued
> logic, as some data bases allow.
I accept that the tools you have used may have been bad.
I will post an example that tells something else.
The meaning of "do not need this facility" depends a lot upon conception
here. I tend to see OnError as related to 3-valued logic (3-valued logic is
about dealing with nil values).
I haven't seen if ... ifnot ... ifnil ....logic implemented anyhere. Any
reference?
Regards
Rom
==^^===============================================================
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4. RE: 'Unknown' and three-valued logic (was: Example where Euphoria ...)
- Posted by rforno at tutopia.com
Nov 28, 2002
For me, the main arguments against 3-valued logic are, in decreasing order
of importance:
1) It appears that there are few, if any, useful applications using this
kind of logic.
2) These possible applications can be handled by ad-hoc routines and data
types. For example, you may select 'F', 'T' and 'N' to represent the 3
values, and write 'not', 'and', 'or', 'xor', 'implication', etc. routines to
compute the results.
3) There is, to my knowledge, no universal consensus about the results of
operations including 'nil', as the recent discussions in this list have
shown.
4) For the application analyst and the programmer, it is much more difficult
thinking in terms of 3 values and the respective operations.
5) It is difficult to draw useful conclusions or actions from the results in
3-valued logic.
6) While operations on strict Boolean logic are implemented very
efficiently, one cannot say the same about 3-valued logic. Especially
operations like and_bits, or_bits, etc., will suffer from severe
inefficiency.
7) If, as suggested, a bit is reserved for 'nil' in each data item, then the
representation ceases to be standard, and difficulties regarding
compatibility will arise.
Regarding the examples, I think that they should be provided by the one
proposing this logic. Up to now, the examples provided by Rom have been not
successful, in my view. The only example that can show a small benefit was
(once more in my view) the very general one about its use in data bases for
non-existing records or fields, particularly under Oracle, but even then I
think it is only of theoretical importance, since I could not find a
convincing practical use for it.
Best wishes.
----- Original Message -----
From: Rom <kjehas at frisurf.no>
To: EUforum <EUforum at topica.com>
Sent: Tuesday, November 26, 2002 1:18 AM
Subject: Re: 'Unknown' and three-valued logic (was: Example where Euphoria
...)
----- Original Message -----
From: <rforno at tutopia.com>
> The problem is not with the tools, but with the tri-valued logic itself.
I need all arguments against 3-valued logic. Please help me
1. Programmers needed 16 bits integers (no space left), not 15 bits integers
2. Because of thant 16/32 bits integer has become common standard. it cannot
be changed...
3. There is no need for such things (thing are either true or false) -
(examples would be appreciated)
4. It would be a terrible thing to handle
5. You don't find it in aother languages either ... proves by itself there
is no need for it..
Anything I have missed here?
Rom
==^^===============================================================
This email was sent to: rforno at tutopia.com
5. RE: 'Unknown' and three-valued logic (was: Example where Euphoria ...)
On 27 Nov 2002, at 18:28, rforno at tutopia.com wrote:
>
> For me, the main arguments against 3-valued logic are, in decreasing order
> of importance:
> 1) It appears that there are few, if any, useful applications using this
> kind of logic.
> 2) These possible applications can be handled by ad-hoc routines and data
> types. For example, you may select 'F', 'T' and 'N' to represent the 3
> values, and write 'not', 'and', 'or', 'xor', 'implication', etc. routines to
> compute the results.
> 3) There is, to my knowledge, no universal consensus about the results of
> operations including 'nil', as the recent discussions in this list have
> shown.
> 4) For the application analyst and the programmer, it is much more difficult
> thinking in terms of 3 values and the respective operations.
> 5) It is difficult to draw useful conclusions or actions from the results in
> 3-valued logic.
> 6) While operations on strict Boolean logic are implemented very
> efficiently, one cannot say the same about 3-valued logic. Especially
> operations like and_bits, or_bits, etc., will suffer from severe
> inefficiency.
> 7) If, as suggested, a bit is reserved for 'nil' in each data item, then the
> representation ceases to be standard, and difficulties regarding
> compatibility will arise.
>
> Regarding the examples, I think that they should be provided by the one
> proposing this logic. Up to now, the examples provided by Rom have been not
> successful, in my view. The only example that can show a small benefit was
> (once more in my view) the very general one about its use in data bases for
> non-existing records or fields, particularly under Oracle, but even then I
> think it is only of theoretical importance, since I could not find a
> convincing practical use for it.
> Best wishes.
I never had need of a 'third' logical boolean state. In fact, I don't
believe it even exists, except as an abstraction. Note that this is
just my opinion. The only other place where I found 'nil' referenced
was on uninitialized variables (as in Lua).
Taking Lua as example, variables have no need to be declared as string,
number, table, etc. until it receives a 'value' of string, number,
table, etc. This way, when created, any variable has a 'nil' (from
Latin nihil - nothing) content. Lua also uses nil as boolean value but
meaning FALSE. A boolean result in Lua can be 1 (TRUE) or nil (FALSE).
There's no third stage. As in Euphoria, all variables must be declared
and initialized before its use, there's no need of a 'nil' value, IMHO.
Kind regards,
-- Euler German
6. RE: 'Unknown' and three-valued logic (was: Example where Euphoria ...)
- Posted by rforno at tutopia.com
Nov 29, 2002
Euler:
It seems to me you got the erroneous impression that I'm advocating for
3-valued logic. Not at all. I was only providing Rom with arguments against
it, on his request.
Oracle (I don't know if this is so for other data-base systems) has a
three-valued logic, and operations on it. Some years ago I worked with this
feature, but never found a practical use for it.
Be good...
----- Original Message -----
From: Euler German <efgerman at myrealbox.com>
Subject: RE: 'Unknown' and three-valued logic (was: Example where Euphoria
...)
>
> On 27 Nov 2002, at 18:28, rforno at tutopia.com wrote:
>
> >
> > For me, the main arguments against 3-valued logic are, in decreasing
order
> > of importance:
> > 1) It appears that there are few, if any, useful applications using this
> > kind of logic.
> > 2) These possible applications can be handled by ad-hoc routines and
data
> > types. For example, you may select 'F', 'T' and 'N' to represent the 3
> > values, and write 'not', 'and', 'or', 'xor', 'implication', etc.
routines to
> > compute the results.
> > 3) There is, to my knowledge, no universal consensus about the results
of
> > operations including 'nil', as the recent discussions in this list have
> > shown.
> > 4) For the application analyst and the programmer, it is much more
difficult
> > thinking in terms of 3 values and the respective operations.
> > 5) It is difficult to draw useful conclusions or actions from the
results in
> > 3-valued logic.
> > 6) While operations on strict Boolean logic are implemented very
> > efficiently, one cannot say the same about 3-valued logic. Especially
> > operations like and_bits, or_bits, etc., will suffer from severe
> > inefficiency.
> > 7) If, as suggested, a bit is reserved for 'nil' in each data item, then
the
> > representation ceases to be standard, and difficulties regarding
> > compatibility will arise.
> >
> > Regarding the examples, I think that they should be provided by the one
> > proposing this logic. Up to now, the examples provided by Rom have been
not
> > successful, in my view. The only example that can show a small benefit
was
> > (once more in my view) the very general one about its use in data bases
for
> > non-existing records or fields, particularly under Oracle, but even then
I
> > think it is only of theoretical importance, since I could not find a
> > convincing practical use for it.
> > Best wishes.
>
>
> I never had need of a 'third' logical boolean state. In fact, I don't
> believe it even exists, except as an abstraction. Note that this is
> just my opinion. The only other place where I found 'nil' referenced
> was on uninitialized variables (as in Lua).
>
> Taking Lua as example, variables have no need to be declared as string,
> number, table, etc. until it receives a 'value' of string, number,
> table, etc. This way, when created, any variable has a 'nil' (from
> Latin nihil - nothing) content. Lua also uses nil as boolean value but
> meaning FALSE. A boolean result in Lua can be 1 (TRUE) or nil (FALSE).
> There's no third stage. As in Euphoria, all variables must be declared
> and initialized before its use, there's no need of a 'nil' value, IMHO.
>
> Kind regards,
>
> -- Euler German
>
>
>
>
7. RE: 'Unknown' and three-valued logic (was: Example where Euphoria ...)
On 28 Nov 2002, at 23:31, rforno at tutopia.com wrote:
>
> Euler:
> It seems to me you got the erroneous impression that I'm advocating for
> 3-valued logic. Not at all. I was only providing Rom with arguments against
> it, on his request.
> Oracle (I don't know if this is so for other data-base systems) has a
> three-valued logic, and operations on it. Some years ago I worked with this
> feature, but never found a practical use for it.
> Be good...
> ----- Original Message -----
Ricardo:
Maybe I didn't express correctly. I was joking. As I never found a
practical use for a three-value logic (too) that I said it was kind of
an abstraction. I should have use an emoticon after it... ;)
Have a nice weekend!
-- Euler
