Implies operator

[antonio]

antonio wrote:
> Kristian Kilpi wrote:
>> On Thu, 16 Nov 2006 13:46:08 +0200, Mariano <rotoshi at yahoo.com> wrote:
>>
>>> == Quote from Stewart Gordon (smjg_1998 at yahoo.com)'s article
>>>> Hasan Aljudy wrote:
>>>> > Mariano wrote:
>>>> <snip>
>>>> >> but the implication makes it far more clear for common day speach
>>>> >>
>>>> >>   if( check_boundaries -> a.length <= max_int )
>>>> >>       process(a);
>>>> >>
>>>> >> makes more sence than
>>>> >>
>>>> >>   if( !check_boundaries || a.length <= max_int )
>>>> >>       process(a);
>>>> </snip>
>>>> What this notation is saying is: If check_boundaries is true, then we
>>>> need to check whether a.length <= max_int - otherwise we needn't 
>>>> bother.
>>>> But still, it isn't exactly the clearest notation.
>>> Yes, it was just an example out of the blue. I think it is clearer, 
>>> and I can't think of a better way.
>>>
>>>> <snip>
>>>> > Yea, it's easy, sure .. but -> has another totally different 
>>>> meaning in
>>>> > C++. Not that I care about C++ anymore, but D, being a C-family
>>>> > language, IMHO, shouldn't do this.
>>>> <snip>
>>>
>>> The notation was just a suggestion. I would prefer =>, but it might 
>>> be confused with >=. Other options are
>>> ==>, -->, and since we have UTF-8 support, why not &#8594; or &#8658;!
>>>
>>> I understand most people don't have the notion of 'implicance' so 
>>> fresh in their heads as with other logical
>>> operators, but I believe this is a consecuence of the imposed 
>>> operators by languages. Having an extra logical
>>> operator would give an edge for the programmer used to it, and won't 
>>> hurt the one who doesn't whant to use it.
>>>
>>> What's more, this operator is far more coherent with the behaviour of 
>>> not revising the second condition if not
>>> needed.
>>>
>>> Who knows, if implemented, it might even become widely used one day.
>>>
>>> Mariano.
>>
>> I haven't used implication anywhere; I'm not 'able' to think x implies 
>> y.. But that's probably because there is no implication operator.
>>
>> Now when I think about it, I have to say that 'x implies y' is a lot 
>> easier to understand than '!x || y'.
>>
>> I cannot say how much I would use it, if there was one. (I'm still not 
>> used to such an operator.)
> 
> The most common example is the null check...
> 
> if( a!=null && a[5]==2 ) {
> }
> 
> we assume "&&" operator is optimized and evaluates left to right... but 
> it's really "dirty" because we use a compiler optimization as a logic 
> functionality.
> 
> for this example, I really will prefer to write
> 
> if( a!=null -> a[5]==2 ) {
> }
> 
> that uses left to right optimized evaluation, but it's more "clean"
> 
> following this, why not
> 
> if( a[5]==2 <- a!=null ) {
> }
> 
> ( "<-" optimized evaluation is right to left )
> 
> 
> 
> One question about && and || optimization:
> 
> Is there some way to specify that I need to evaluate the 2 sides of the 
> comparer?
> 
> (something like &&& or ||| )
> 
> note:  "if( And( left() , right() ) )" or similar is not a solution :-)
> 
> Thanks
> 
> 
> 
> 
SORRY...

"a!=null -> a[5]==2"

is not the same than

"a!=null && a[5]==2"...

my fault :-(