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B.5 Interfacing with Fortran

The facilities relevant to interfacing with the Fortran language are the package Interfaces.Fortran and support for the Import, Export and Convention pragmas with convention_identifier Fortran.
The package Interfaces.Fortran defines Ada types whose representations are identical to the default representations of the Fortran intrinsic types Integer, Real, Double Precision, Complex, Logical, and Character in a supported Fortran implementation. These Ada types can therefore be used to pass objects between Ada and Fortran programs.
Static Semantics
The library package Interfaces.Fortran has the following declaration:
       with Ada.Numerics.Generic_Complex_Types;  -- see G.1.1
       pragma Elaborate_All(Ada.Numerics.Generic_Complex_Types);
       package Interfaces.Fortran is
          pragma Pure(Fortran);
          type Fortran_Integer is range implementation-defined;
          type Real             is digits implementation-defined;
          type Double_Precision is digits implementation-defined;
          type Logical is new Boolean;
          package Single_Precision_Complex_Types is
             new Ada.Numerics.Generic_Complex_Types (Real);
          type Complex is new Single_Precision_Complex_Types.Complex;
          subtype Imaginary is Single_Precision_Complex_Types.Imaginary;
          i : Imaginary renames Single_Precision_Complex_Types.i;
          j : Imaginary renames Single_Precision_Complex_Types.j;
          type Character_Set is implementation-defined character type;
          type Fortran_Character is array (Positive range <>) of Character_Set;
          pragma Pack (Fortran_Character);
          function To_Fortran (Item : in Character) return Character_Set;
          function To_Ada (Item : in Character_Set) return Character;
          function To_Fortran (Item : in String) return Fortran_Character;
          function To_Ada     (Item : in Fortran_Character) return String;
          procedure To_Fortran (Item       : in String;
                                Target     : out Fortran_Character;
                                Last       : out Natural);
          procedure To_Ada (Item     : in Fortran_Character;
                            Target   : out String;
                            Last     : out Natural);
       end Interfaces.Fortran;
The types Fortran_Integer, Real, Double_Precision, Logical, Complex, and Fortran_Character are Fortran-compatible.
The To_Fortran and To_Ada functions map between the Ada type Character and the Fortran type Character_Set, and also between the Ada type String and the Fortran type Fortran_Character. The To_Fortran and To_Ada procedures have analogous effects to the string conversion subprograms found in Interfaces.COBOL.
Implementation Requirements
An implementation shall support pragma Convention with a Fortran convention_identifier for a Fortran-eligible type (see B.1).
Implementation Permissions
An implementation may add additional declarations to the Fortran interface packages. For example, the Fortran interface package for an implementation of Fortran 77 (ANSI X3.9-1978) that defines types like Integer*n, Real*n, Logical*n, and Complex*n may contain the declarations of types named Integer_Star_n, Real_Star_n, Logical_Star_n, and Complex_Star_n. (This convention should not apply to Character*n, for which the Ada analog is the constrained array subtype Fortran_Character (1..n).) Similarly, the Fortran interface package for an implementation of Fortran 90 that provides multiple kinds of intrinsic types, e.g. Integer (Kind=n), Real (Kind=n), Logical (Kind=n), Complex (Kind=n), and Character (Kind=n), may contain the declarations of types with the recommended names Integer_Kind_n, Real_Kind_n, Logical_Kind_n, Complex_Kind_n, and Character_Kind_n.
Implementation Advice
An Ada implementation should support the following interface correspondences between Ada and Fortran:

Example of Interfaces.Fortran:
       with Interfaces.Fortran;
       use Interfaces.Fortran;
       procedure Ada_Application is
          type Fortran_Matrix is array (Integer range <>,
                                        Integer range <>) of Double_Precision;
          pragma Convention (Fortran, Fortran_Matrix);    -- stored in Fortran's
                                                          -- column-major order
          procedure Invert (Rank : in Fortran_Integer; X : in out Fortran_Matrix);
          pragma Import (Fortran, Invert);                -- a Fortran subroutine
          Rank      : constant Fortran_Integer := 100;
          My_Matrix : Fortran_Matrix (1 .. Rank, 1 .. Rank);
          My_Matrix := ...;
          Invert (Rank, My_Matrix);
       end Ada_Application;

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