* Fun: the Ada assignment operator is an alias of the equivalence operator
@ 2011-05-28 0:48 Yannick Duchêne (Hibou57)
2011-05-28 7:25 ` Dmitry A. Kazakov
0 siblings, 1 reply; 6+ messages in thread
From: Yannick Duchêne (Hibou57) @ 2011-05-28 0:48 UTC (permalink / raw)
Hello,
A very light topic: I've just discovered the Ada / Pascal assignment
operator, is one of the alias of the logical-equivalence or defined-as
operator, that is, “ := ” is an alias of “ ≡ ”. As was trying to makeup my
mind about some ambiguities in the use which is made of “ ≡ ” when I
landed to this Wikipedia page :
http://en.wikipedia.org/wiki/List_of_logic_symbols
This is a rather good choice which was made… would have been a perfect
choice is this was not used for side effects (let say this is just the
interpretation context which slightly vary :-D ).
--
“Syntactic sugar causes cancer of the semi-colons.” [Epigrams on
Programming — Alan J. — P. Yale University]
“Structured Programming supports the law of the excluded muddle.” [Idem]
“c++; /* this makes c bigger but returns the old value */” [Anonymous]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Fun: the Ada assignment operator is an alias of the equivalence operator
2011-05-28 0:48 Fun: the Ada assignment operator is an alias of the equivalence operator Yannick Duchêne (Hibou57)
@ 2011-05-28 7:25 ` Dmitry A. Kazakov
2011-05-28 8:02 ` Yannick Duchêne (Hibou57)
0 siblings, 1 reply; 6+ messages in thread
From: Dmitry A. Kazakov @ 2011-05-28 7:25 UTC (permalink / raw)
On Sat, 28 May 2011 02:48:29 +0200, Yannick Duchêne (Hibou57) wrote:
> A very light topic: I've just discovered the Ada / Pascal assignment
> operator, is one of the alias of the logical-equivalence or defined-as
> operator, that is, “ := ” is an alias of “ ≡ ”.
I didn't see that usage of ":=" ("Defined-as" is not same "equivalent").
For "defined-as" I saw "=" with a small triangle or word "def" under it. In
grammar definitions "::=" or "->".
≡ is indeed used as equivalent/tautological.
> This is a rather good choice which was made… would have been a perfect
> choice is this was not used for side effects (let say this is just the
> interpretation context which slightly vary :-D ).
Assignment is not a logical operation, variables are not logical
predicates. Even
A := B;
Post (A = B); -- Not necessarily true.
(A variable is a mapping of the program state onto the domain values set.
Assignment merely denotes a state transition.)
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Fun: the Ada assignment operator is an alias of the equivalence operator
2011-05-28 7:25 ` Dmitry A. Kazakov
@ 2011-05-28 8:02 ` Yannick Duchêne (Hibou57)
2011-05-28 9:03 ` Dmitry A. Kazakov
0 siblings, 1 reply; 6+ messages in thread
From: Yannick Duchêne (Hibou57) @ 2011-05-28 8:02 UTC (permalink / raw)
Le Sat, 28 May 2011 09:25:40 +0200, Dmitry A. Kazakov
<mailbox@dmitry-kazakov.de> a écrit:
> I didn't see that usage of ":=" ("Defined-as" is not same "equivalent").
>
> For "defined-as" I saw "=" with a small triangle or word "def" under it.
http://www.unicode.org/charts/PDF/U2200.pdf agree with you
Says
225C ≜ DELTA EQUAL TO = equiangular = equal to by definition
2261 ≡ IDENTICAL TO
(a bit ambiguous)
> Assignment is not a logical operation, variables are not logical
> predicates.
Nor "defined-as" is ;)
":=" would be OK for constant, makes Ada looks a bit more functional :p
--
“Syntactic sugar causes cancer of the semi-colons.” [Epigrams on
Programming — Alan J. — P. Yale University]
“Structured Programming supports the law of the excluded muddle.” [Idem]
“c++; /* this makes c bigger but returns the old value */” [Anonymous]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Fun: the Ada assignment operator is an alias of the equivalence operator
2011-05-28 8:02 ` Yannick Duchêne (Hibou57)
@ 2011-05-28 9:03 ` Dmitry A. Kazakov
2011-05-28 9:19 ` Yannick Duchêne (Hibou57)
0 siblings, 1 reply; 6+ messages in thread
From: Dmitry A. Kazakov @ 2011-05-28 9:03 UTC (permalink / raw)
On Sat, 28 May 2011 10:02:51 +0200, Yannick Duch�ne (Hibou57) wrote:
>> Assignment is not a logical operation, variables are not logical
>> predicates.
> Nor "defined-as" is ;)
>
> ":=" would be OK for constant, makes Ada looks a bit more functional :p
I think it is a widely shared misconception that immutability has anything
to do with that. [Functional is not an answer, whatever the question was
(:-))]
No, even an initialized constant is not necessarily equivalent to its
initializing expression. Obvious examples:
I : constant Integer := Get (File);
X : constant Float := Random (Dice);
T : constant Time := Clock;
Another point is that equivalence itself is an abstract operation with the
semantics undefined in general.
Mathematical equivalence = is not analogous to "=" operation defined on
objects. Rather it is:
1. Values equivalence (values do not belong to the program). I.e. you can
say that the value of the variable A is equivalent to the value of the
variable B. Which is unrelated [not required] to whether A=B yields True or
False.
2. Program equivalence. You can say that two programs are equivalent in
some [limited] sense, e.g. when the compiler optimizes the code, or when
you modify the program.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Fun: the Ada assignment operator is an alias of the equivalence operator
2011-05-28 9:03 ` Dmitry A. Kazakov
@ 2011-05-28 9:19 ` Yannick Duchêne (Hibou57)
2011-05-28 9:58 ` Dmitry A. Kazakov
0 siblings, 1 reply; 6+ messages in thread
From: Yannick Duchêne (Hibou57) @ 2011-05-28 9:19 UTC (permalink / raw)
Le Sat, 28 May 2011 11:03:25 +0200, Dmitry A. Kazakov
<mailbox@dmitry-kazakov.de> a écrit:
> I think it is a widely shared misconception that immutability has
> anything
> to do with that. [Functional is not an answer, whatever the question was
> (:-))]
>
> No, even an initialized constant is not necessarily equivalent to its
> initializing expression. Obvious examples:
>
> I : constant Integer := Get (File);
> X : constant Float := Random (Dice);
> T : constant Time := Clock;
Right Er Professor, sure ":=" does not introduce a macro :p So, what about
“defined-as the realization-of” ?
> 2. Program equivalence. You can say that two programs are equivalent in
> some [limited] sense, e.g. when the compiler optimizes the code, or when
> you modify the program.
Equivalent by realization (modulus some canonicalization of the output) ?
--
“Syntactic sugar causes cancer of the semi-colons.” [Epigrams on
Programming — Alan J. — P. Yale University]
“Structured Programming supports the law of the excluded muddle.” [Idem]
“c++; /* this makes c bigger but returns the old value */” [Anonymous]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Fun: the Ada assignment operator is an alias of the equivalence operator
2011-05-28 9:19 ` Yannick Duchêne (Hibou57)
@ 2011-05-28 9:58 ` Dmitry A. Kazakov
0 siblings, 0 replies; 6+ messages in thread
From: Dmitry A. Kazakov @ 2011-05-28 9:58 UTC (permalink / raw)
On Sat, 28 May 2011 11:19:09 +0200, Yannick Duchêne (Hibou57) wrote:
> Le Sat, 28 May 2011 11:03:25 +0200, Dmitry A. Kazakov
> <mailbox@dmitry-kazakov.de> a écrit:
>> I think it is a widely shared misconception that immutability has
>> anything
>> to do with that. [Functional is not an answer, whatever the question was
>> (:-))]
>>
>> No, even an initialized constant is not necessarily equivalent to its
>> initializing expression. Obvious examples:
>>
>> I : constant Integer := Get (File);
>> X : constant Float := Random (Dice);
>> T : constant Time := Clock;
>
> Right Er Professor, sure ":=" does not introduce a macro :p
"Lazy" would be a better word than "macro".
> So, what about
> “defined-as the realization-of” ?
Well, declaration of an immutable variable defines it in a scope. The point
is that realization, which looks like just another word for "value", cannot
define [immutable] variable. A variable can be defined *to have* some
value, but variable is not a value. Value is a "meaning" of a variable in
some context. In mathematics both sides of "defined-as" are same sort of
beasts.
BTW, just for fun:
Huh : constant Boolean := Halt (P); -- Is Huh defined? (:-))
>> 2. Program equivalence. You can say that two programs are equivalent in
>> some [limited] sense, e.g. when the compiler optimizes the code, or when
>> you modify the program.
> Equivalent by realization (modulus some canonicalization of the output) ?
Indistinguishable by certain means, e.g. within some formal model, like
black box etc.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2011-05-28 9:58 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-05-28 0:48 Fun: the Ada assignment operator is an alias of the equivalence operator Yannick Duchêne (Hibou57)
2011-05-28 7:25 ` Dmitry A. Kazakov
2011-05-28 8:02 ` Yannick Duchêne (Hibou57)
2011-05-28 9:03 ` Dmitry A. Kazakov
2011-05-28 9:19 ` Yannick Duchêne (Hibou57)
2011-05-28 9:58 ` Dmitry A. Kazakov
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox