Re: Puzzled by SPARK global aspect

[digitig <digitig@gmail.com>]

On Saturday, July 1, 2017 at 4:51:22 PM UTC+1, Anh Vo wrote:
> On Friday, June 30, 2017 at 2:29:38 PM UTC-7, digitig wrote:
> > Suppose in my package specification I have
> > 
> >    type Quadrant_Specification_Array is 
> >    array(Global.Quadrant_X_Index'Range, Global.Quadrant_Y_Index'Range) 
> >    of Quadrant_Specification;
> > 
> > (With QuadrantSpecification being a record type) and in my package body I have:
> > 
> >    function N_Total_Klingons return Global.Klingon_Counter
> >        with
> >          Refined_Global => (Input => Quadrant_Specifications)
> >    is
> >       Total: Global.Klingon_Counter := 0;
> >    begin
> >       for X in Quadrant_Specifications'Range loop
> >          for Y in Quadrant_Specifications'Range(2) loop
> >             Total := Total + Quadrant_Specifications(X, Y).N_Klingons;
> >          end loop;
> >       end loop;
> >       return Total;
> >    end N_Total_Klingons;
> > 
> > Spark gives me an error
> >   useless refinement, subprogram "N_Total_Klingons" does not depend on abstract state with visible refinement
> > 
> > But if I take the Refined_Global specification out I get the error
> > 
> >   "Quadrant_Specifications" must be listed in the Global aspect of "N_Total_Klingons"
> > 
> > I feel I'm losing either way - if I do specify it I'm wrong, if I don't specify it I'm wrong.
> > 
> > How *do* I fix this?
> 
> It is pretty hard to suggest advice since it is not a complete minimal code. In addition, I rather see the code instead of guessing. I would say your codes involve package Abstract State aspect.
> 
> Anh Vo

Here's a fairly minimal spec and body, then, which gives the problem I describe:

---- main.ads ----
package Main
with
SPARK_Mode => On
  is
type Quadrant_Specification is record
   N_Klingons: Integer := 0;
end record;

subtype Klingon_Counter is Integer range 0..20;

   type Quadrant_Specification_Array is
     array(1..8, 1..8)
     of Quadrant_Specification;


   function N_Total_Klingons return Integer
     with
       Global => null,
       Depends => (N_Total_Klingons'Result => null),
     Pre => True;

end Main;

---- Main.adb ----
package body Main
with
  SPARK_Mode => On
is
   Quadrant_Specifications: Quadrant_Specification_Array;

   function N_Total_Klingons return Integer
--           with
--             Refined_Global => Quadrant_Specifications
   is
      Total: Integer := 0;
   begin
      for X in Quadrant_Specifications'Range loop
         for Y in Quadrant_Specifications'Range(2) loop
            Total := Total + Quadrant_Specifications(X, Y).N_Klingons;
         end loop;
      end loop;
      return Total;
   end N_Total_Klingons;
end Main;