gcc/ada/libgnat/s-spcuop.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --           S Y S T E M . S P A R K . C U T _ O P E R A T I O N S          --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --             Copyright (C) 2022-2023, Free Software Foundation, Inc.      --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  By and So are connectors used to manually help the proof of assertions by
  33 --  introducing intermediate steps. They can only be used inside pragmas
  34 --  Assert or Assert_And_Cut. They are handled in the following way:
  35 --
  36 --  *  If A and B are two boolean expressions, proving By (A, B) requires
  37 --     proving B, the premise, and then A assuming B, the side-condition. When
  38 --     By (A, B) is assumed on the other hand, we only assume A. B is used
  39 --     for the proof, but is not visible afterward.
  40 --
  41 --  *  If A and B are two boolean expressions, proving So (A, B) requires
  42 --     proving A, the premise, and then B assuming A, the side-condition. When
  43 --     So (A, B) is assumed both A and B are assumed to be true.
  44
  45 package System.SPARK.Cut_Operations with
  46   SPARK_Mode,
  47   Pure,
  48   Always_Terminates
  49 is
  50
  51    function By (Consequence, Premise : Boolean) return Boolean with
  52      Ghost,
  53      Global => null;
  54
  55    function So (Premise, Consequence : Boolean) return Boolean with
  56      Ghost,
  57      Global => null;
  58
  59 end System.SPARK.Cut_Operations;