Re: Is there a language that Dijkstra liked? (was: Re: Software landmines (loops))

[Ehud Lamm <mslamm@mscc.huji.ac.il>]

On Wed, 28 Oct 1998, Pat Rogers wrote:

> One does have to be careful, though.  Consider:
> 
> function Next( This : Some_Discrete_Type ) return
> Some_Discrete_Type is
> begin
>   return Some_Discrete_Type'Succ(This);
> exception
>   when Constraint_Error =>
>     return Some_Discrete_Type'First;
> end Next;
> 
>  In such cases the explicit, hand-coded check is
> preferable, IMHO:
> 
> function Next( This : Some_Discrete_Type ) return
> Some_Discrete_Type is
> begin
>   if This = Some_Discrete_Type'Last then
>     return Some_Discrete_Type'First;
>   else
>     return  Some_Discrete_Type'Succ(This);
>   end if;
> end Next;
> 

In this example, I for one would think both approaches are viable. Maybe I
would even prefer the IF approach. 

This is not the example for misusing valdity checks. 

What I find ugy is things like this:

i:integer

if i<0 then <some error handling>

instead of
 i:Natural

This kind of coding style doesn't allow the reader to stop checking for
himself the i is indeed always non negative.

Ehud Lamm     mslamm@mscc.huji.ac.il