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Date: Tue, 30 Dec 2008 15:11:17 +0100
From: Georg Bauhaus <rm.tsoh.plus-bug.bauhaus@maps.futureapps.de>
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Subject: Pascal ranges  (was: Selective suppression of warnings --- gnat on
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Date: 2008-12-30T15:11:22+01:00
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(see below) wrote:

>>>  The Pascal declaration:
>>>
>>>   type  somerange = 1..10;
>>>
>>> Means, in Ada:
>>>
>>>    SUBtype  somerange is Integer range 1..10;

> The point is that in Pascal they are NOT different types, so if one wants to
> mirror the semantics of the Pascal program - which is presumably the reason
> for translating it - one must do as I say.

Maybe, then, type mapping from Pascal ranges to Ada ranges,
selecting either types or subtypes,
will be an interesting switch to add to P2Ada?  I now get

-- Translated by (New) P2Ada v. 15-Nov-2006
-- ...
-- formatted by iccfmt_nt.exe

package stage3 is

   type somerange is range 1..10;

   type somestruct is
      record
         null;
      end record;

   function test(a : somerange) return integer;

end stage3;


for the Turbo Pascal input file

unit stage3;

interface

   type
      somerange = 1..10;
      somestruct = record  end;

   function test(a: somerange) : integer;

implementation
 ...
end.

Bits of history tell that programmers started protests when Modula/Wirth
introduced different, incompatible types such as INTEGER
and CARDINAL, together with type conversions and type cheats (pretty
much the same as instances of Unchecked_Conversion, I guess?)

Because, it seems, the protesters would have to type more characters
and state explicitly the conversions that they had previously just
thought about carefully and then delegated to the Depepartment of
The Obvious.


> Even writing afresh in Ada, it is very unlikely indeed that one would want
> EVERY subrange to be a separate type.

OK, but OTOH, is a program improved when by default
different Pascal ranges are mapped to Ada ranges of distinct
types?  I think, yes, in case one assumes Ada requires stating
assumptions explicitly by default:
If Pascal's integer ranges are not made for expressing
different types, then maybe Pascal programmers do their best
and carefully mix objects of logically distinct integer types
only when a conversion is logically valid. If a compiler can
help with this in case ranges are made different types by
default, why not?  (I.e., if a subtype constraint is enough
distinction, the type declarations would have to be turned
into subtype declarations by hand, after the automatic
translation has turned Pascal ranges into different Ada
types.)