Re: Puzzled by SPARK global aspect

[Anh Vo <anhvofrcaus@gmail.com>]

On Saturday, July 1, 2017 at 11:25:20 AM UTC-7, digitig wrote:
> 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:
> 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;

Both Global and Depends are under umbrella of Abstract_State at the package level. Therefore, Abstract_State must be defined below. Note that Package_State is an arbitrary name.

package body Main 
  with 
    SPARK_Mode => On,
    Refined_State => (Package_State => Quadrant_Specifications)
is 
-- ...

In addition, Global and Depends are defined below because this function depends on local global variable.

   function N_Total_Klingons return Integer 
     with 
       Global => Package_State,
       Depends => (N_Total_Klingons'Result => Package_State)
   is
   -- ...

In the package body Refined_State must be defined to use Quadrant_Specifications as shown below.

package body Main 
  with 
    SPARK_Mode => On,
    Refined_State => (Package_State => Quadrant_Specifications)
is 
-- ...

Moreover, Refined_Global and Refined_Depends aspects must be declared to use the array variable Quadrant_Specifications.