Re: Modular type. What is it and why?

[Ole-Hjalmar Kristensen <ohk@maestro.clustra.com>]

"Mike Silva" <mjsilva@jps.net> writes:

> David C. Hoos, Sr. wrote in message <7eb2iq$jc3@hobbes.crc.com>...
> <....>
> >There are many uses for such a type -- e.g., the index of a circular array,
> or a representation of the days of the week...
> 
> One of the little "goodies" I discovered in coming from C to Ada are modular
> types.  I often had to write code like:
> 
> switch ( key )
> {
>    case ARROW_DOWN:
>       if ( index < ( NUM_ELEMENTS - 1 ) )
>          index++;
>       else
>          index = 0;
>       break;
>    case ARROW_UP:
>       if ( index > 0 )
>          index = NUM_ELEMENTS - 1;
>       else
>          index--;
>       break;
> }
> 
> Now with Ada I'll be able to write (assuming 'index' is the appropriate
> modular type):
> 
> case ( key ) is
>    when ARROW_DOWN =>
>       index := index + 1;
>    when ARROW_UP =>
>       index := index - 1;
> end case;
> 
> Now -that's- what I call progress!
> 
> Mike
> 
> 
> 
> 

Yes, this is a good illustration of modular types. However, what do
you do if NUM_ELEMENTS change? 
Maybe modular types isn't the right choice in this case.

-- 
E pluribus Unix