Bools reloaded

[Bruno Medeiros]

Don Clugston wrote:
> Tom wrote:
>> In article <du71jc$1e9h$1 at digitaldaemon.com>, Bruno Medeiros says...
>>> Walter Bright wrote:
>>>> "Tom" <Tom_member at pathlink.com> wrote in message 
>>>> news:du049t$2uv2$1 at digitaldaemon.com...
>>>>> Yes, PLEASE, WHY?? Just ONE argument against pure bools, only one 
>>>>> and I shut my
>>>>> mouth forever!
>>>> One should be very careful about stepping away from C's implicit 
>>>> promotion rules for a language that aims to be a successor to C. C 
>>>> absolutely *buried* Pascal.
>>>>
>>> Uuh, I'm not sure what Tom meant by "pure bools", nor I'm sure what 
>>> you meant by "C's implicit promotion rules" (as C doesn't even have a 
>>> bool). But ok, nevermind, let's pause for a moment, and get our facts 
>>> straight.
>>>
>>> What exactly is it in bools that you Walter, want and not want?
>>> I already know that the ability to write 'while(1)' as the same as 
>>> 'while(true)' is one of them, but, anything more?
>>> Is the behaviour of having an "implicit promotion" something you want 
>>> too?
>>> If so, promotion from where, from int to bool, or from bool to int?
>>> Do you want or not want bool numeric operations to be an error (like 
>>> boolA / boolB*2) ?
>>
>> You should read the latest posts about this stuff (the most with 
>> subject "Re:
>> DMD 0.148 release"). It's all said there. By "pure bools" I mean the 
>> *purist
>> kind* of boolean type. A boolean type that abstracts us from the 
>> implementation.
> 
> Sorry, that's still not clear.
> Bruno is right, terms like "pure bools" or "purist bools" are vague, you 
> can't expect everyone to know what you mean.
> 
> For example: do you want "&" to be legal for bool types, or just "&&"?
> (they mean very different things for integers). "&" normally means 
> "bitwise and", but a pure bool doesn't have any bits.
> Is it legal to cast from a bool to some other type?
> 
>  > A boolean type that abstracts us from the implementation.
> 
> No abstraction is perfect. Does a bool have a defined bit 
> representation? (If you say 'no' to this, then I don't think a bool 
> could be used in an extern function, you'd always have to convert it to 
> int or something).
> 
> You need a comprehensive list of which operations are legal, and which 
> are not.

Exactly, the "pure bools" must be defined by a set of language 
behaviors. Derek made a post some time ago with one such definition 
(news://news.digitalmars.com:119/14shfnb64x5o2.17cec6fac7wnu.dlg@40tude.net).

However, the problem is, and the reason I opened this thread, that in 
the previous discussion people started getting lost in a too vague or 
incongruous debate of "pure bools" vs. being able to use "while(1)" and 
implicit conversions and whatnot (arguing about things that are not on 
the same level).
What I'm trying to say is, that of that set of bool behaviors, it is not 
an all or nothing situation, it is a gradient of behaviors. Just a part 
of them can be implemented, and if all Walter wants is the ability to do 
"while(1)" or 'implicit conversion of integers to bool' (which are the 
only counter-points I've seen so far), then there is still a lot of 
other things that can me made to improve bool:

We could have:
* Conditional expressions should be of type bool
* Integers can be implicitly converted to bool, as Walter wants. (where 
0 is false, the rest is true). This allows for "while(1)" .
* Pointer and references can be implicitly converted too (where null is 
false, the rest is true). This allows for "if(objFoo)" .
* No numeric operations are allowed on bool, just boolean operations.
* bool can only be explicitly cast to a numeric type.
* Regardless of bool implementation, it has only two abstract states: 
true or false, and conversions from int should be aware of that. For 
instance this should 'then':
   if (2==true) writefln("then");  // doesnt "then" :(

It won't be the "purest" of bools (like Java or C# or other languages), 
because of the second feature, but it's still a lot better than what we 
have. Walter what's your take? Do you have any problem with any of these 
behaviors?

-- 
Bruno Medeiros - CS/E student
"Certain aspects of D are a pathway to many abilities some consider to 
be... unnatural."