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From: "G.B." <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Substrings as argument to procedures/functions
Date: Wed, 13 Apr 2016 13:22:38 +0200
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Date: 2016-04-13T13:22:38+02:00
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On 12.04.16 10:25, reinkor wrote:
> Dear All,
>
> I believed that if a substring is an argument to a subroutine,
> then its "range" would start at 1 (and not inherited from the calling program).
> But this seems not to be the case.

> Is this correct? And in case, is it "good" ? :-)

It is a good idea, I think, not to be mislead by programming
languages that don't have expressions for iteration at all,
nor "sequence types", only emulations. That these are prone to
errors has been mentioned in this thread.  Consider

    for K in A'Range loop
       ... A(K) ...
    end loop;

or, more recently found in Ada,

    for El of A loop
       ... El ...
    end loop;

This most frequently used loop that does sequence processing
does not refer to any specific bound on A. No assumptions, or
checks are being programmed. It is safe and efficient.

Similarly, if I were using a recursive LISP style approach,
positions, or index values, do not matter either:

    function Count (A : String; X : Character) return Integer is

       function Count_Loop (K : Positive) return Natural is
       begin
          if K <= A'Last then
             return "+" (Boolean'Pos ("=" (A(K), X)),
                         Count_Loop (Positive'Succ (K)));
          else
             return 0;
          end if;
       end Count_Loop;

    begin
       return Count_Loop (A'First);
    end Count;