Re: ICFP Programming Contest virtual machine in Ada

[Georg Bauhaus <bauhaus@futureapps.de>]

Javier Miranda wrote:
> 
> On Aug 1, 2006, at 4:43 PM, Georg Bauhaus wrote:
> 
>> Alas, this code cannot be compiled with a plain Ada compiler
>> as it uses non-Ada 'Img (which is brief, though).
> 
> Considering T the type of the object to which you apply this
> attribute, this is a GNAT attribute that is equivalent to
> T'Image (Obj).

Yes, but 'Img was invented for quickly writing debugging
expressions, IIRC, not for writing standard Ada expressions.

It might be worth pointing out that T must be a scalar type.

> For example, being V a variable containing an integer value,
> instead of writing Integer'Image (V) you can just write V'Img.

No, you can't write V'Img because 'Img is a GNAT implementation
defined attribute ;-) For a standard Ada program, you must write
Integer'Image(V).

Pragma Extensions_Allowed(Off) does not seem to turn this 'Img
extension of. Is there a switch to instruct gnatmake to warn
about implementation defined attributes? Or more generally,
something with an intent similar to -gnato, or -gnat83/95/05,
that makes GNAT reject non-standard constructs? 

(I have found some advice in the GNAT documentation
to not use implementation defined pragmas when portability
is an issue; given the qualities of GNAT, I should think that
it can categorize the pragmas found in source text, and inform
about the result.)


-- Georg