Re: advantages or disadvantages of ADA over pascal or modula

[Martin Klaiber <martinkl@zedat.fu-berlin.de>]

Gautier <gautier_niouzes@hotmail.com> wrote:
> Martin Klaiber:

>> First, it would be nice, if an object in Ada would know it's own
>> variables without naming them explicitly.

> In fact, you are missing BP's prefixed OO notation (object.Method).
> You will certainly find fierce debates in c.l.a archives about it.

Yes, I've read some of these debates. I don't prefer one notation over
the other. Both have their advantages and disadvantages IMHO.

> The explicit has maybe the merit of readability over concision

Hm, depends on. Redundancy can affect readability too.

>> Second, it would be nice, if Ada would allow to change internal
>> variables of an object also in functions.

> Also subject to debates... you say it's intuitive because you are
> accustomed to it. 

Yes, that might be true.

> But look at your example. Normally, the basic role of a function is to
> give a value in function of other (the parameters).

Here the parameter is in the function-name. I could have written it
also as (skipped a bit to keep the line short):

  function IncMonth (Calender : ...; Days : Positive) return boolean;

> In your case the main information is what you do to "Calendar" and the
> result has a minor role - quite strange...

Well, this depends on how you want to use such functions. I like to use
them like that:

  if IncMonth (Calendar) = true then
    Update (Anything);
  end if;

> It would be more elegant and intuitive (and also efficient) to write

>  procedure IncMonth (Calendar : in out type_Calendar) is
>  begin
>    if Calendar.Month = 12 then
>      IncYear (Calendar);
>      Calendar.Month := 1;
>    else
>      Calendar.Month := Calendar.Month + 1;
>    end if;
>  end IncMonth;

>  procedure function IncYear (Calendar : in out type_Calendar) is
>  begin
>    if Calendar.Year < 3000 then
>      Calendar.Year := Calendar.Year + 1;
>    else
>      raise Year_out_of_range;
>    end if;
>  end IncYear;

Will this really work like that? Calendar.Month must not be set to 1
if IncYear fails. Does this mean, if exception Year_out_of_range is
raised, the rest of the code in IncMonth will be skipped?

> Don't forget, you have the exceptions... it saves a lot of transporting
> error codes and acrobatic expressions...

Yes, these exceptions are phantastic. I really have to get used to them.

Martin