How to use the Ada bindings
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## How to use the Ada bindings

### Ada 95 versus Ada 2005

The bindings will work for either Ada 95 or Ada 2005 but there is a slightly subtle point regarding the use and declaration of vectors and matrices. The package `PLplot_Auxiliary` declares the types

        type Real_Vector is array (Integer range <>) of Long_Float;
        type Real_Matrix is array (Integer range <>, Integer range <>) of Long_Float;

These declarations mimic exactly the declarations described in Annex G.3, Vector and Matrix Manipulation, of the Ada 2005 reference manual when the generic package therein described is specialized for `Long_Float`. The reason for this approach is to avoid requiring the user program to `with` `Ada.Numerics.Long_Real_Arrays` simply to gain access to these types and in the process require linking to the BLAS and LAPACK numerical libraries.

Ada 2005 introduced an annex G.3 which formally defines vector and matrix support to Ada, along with some common mathematical operations on those types. (This feature is a specific to vectors and matrices and extends the usual array apparatus.) The Ada PLplot user has a choice on how to deal with this. The default, as described in `PLplot_Auxiliary.ads`, has `Real_Vector` and `Real_Matrix` declared therein, separate from the Ada 2005 declarations. This allows the widest compatibility and does not require an Ada 2005 compiler. However, many users will want to gain the benefit of the built-in declarations of Ada 2005. This is easily done: Read the short comments in `PLplot_Auxiliary.ads` on how to comment-out two lines and uncomment three lines. Either configuration will compile correctly, but depending on the Cmake configuration to expose an Ada 2005 compiler in the later case. (Note that at some points in the documentation, Ada 2005 is referred to as Ada 2007, including some Cmake flags.)

This policy was changed in SVN version 11153. Before this, the type of compiler (Ada 95 or Ada 2005) had to be specified at the time that PLplot was built, and in the case of Ada 2005, the BLAS and LAPACK libraries had to be present and were subsequently linked.

### GNAT versus non-GNAT

The bindings were made using the GNAT compiler and there is a slight dependence on that compiler. Specifically, the `Unrestricted_Access` attribute of GNAT was used in making the function `Matrix_To_Pointers` in `plplotthin.adb` and in a few callbacks. `Matrix_To_Pointers` is called whenever an Ada matrix (2D array) is passed to a PLplot subroutine. For more about `Unrestricted_Access attribute`, see Implementation Defined Attributes in the GNAT Reference Manual. This dependency shouldn't be difficult to remove by either incorporating the GNAT code which implements it, by following the TO-DO comment near the function definition in `plplotthin.adb`, or by providing the proper aliasing.

Another GNAT dependency is used to parse command line arguments in a C-like way.

Pragma Warnings (Off, "some text") and Pragma Warnings (On, "some text") are used in the bindings to suppress warnings about a particular method used to interface with C code. These pragmas are also used in Ada Examples 21 to suppress a particular warning. Pragma Warnings is a GNAT extension. Non-GNAT usage could simply remove these pragmas with the resulting warnings ignored as they are benign.

Most of the GNAT dependencies can be found by searching the source code for "`GNAT`", "`Unrestricted_Access` and `Pragma Warnings`."

The GNAT dependence, though slight, will no doubt frustrate users of other Ada compilers. We welcome comments from those users, especially comments with specific suggestions on how to remove any GNAT-specific usages.

### Sample command line project

It is instructive to present a simple example that can be compiled and run from the command line. Although this example is specific to one installation, it should be fairly straightforward to adapt it to another installation. Toward that end, it is helpful to understand the PLplot lingo of "build directory" and "installation directory."

Here is a simple program that will generate a plot of part of a parabola.

     with
        PLplot_Auxiliary,
        PLplot;
     use
        PLplot_Auxiliary,
        PLplot;
     procedure Simple_Example is
        x, y : Real_Vector(-10 .. 10);
     begin
        for i in x'range loop
           x(i) := Long_Float(i);
           y(i) := x(i)**2;
        end loop;
        Initialize_PLplot; -- Call this only once.
        Simple_Plot(x, y); -- Make the plot.
        End_PLplot;        -- Call this only once.
     end Simple_Example;

Next is a bash script that will compile, bind, and link it. It is installation-specific in that paths to the GNAT compiler, PLplot libraries, and BLAS (Basic Linear Algebra System) and LAPACK (Linear Algebra Package) are hard-coded. You will have to adjust the paths to fit your installation. Some Linux installations which have GNAT 4.3 or later (Ada 2005) preinstalled might have already set the paths to the BLAS and LAPACK libraries.

(Note that the G.3 Annex of Ada 2005, in the GNAT version, depends heavily on BLAS and LAPACK. These packages are tried-and-true packages that are available from several places in either C or Fortran versions. The present example is specific to OS X which has both C and Fortran versions preinstalled.)

     #!/bin/bash
     /usr/local/ada-4.3/bin/gnatmake simple_example.adb \
     -aI/usr/local/plplot_build_dir/bindings/ada \
     -aL/usr/local/plplot_build_dir/bindings/ada/CMakeFiles/plplotadad.dir \
     -largs \
     /usr/local/plplot/lib/libplplotd.dylib \
     /Developer/SDKs/MacOSX10.4u.sdk/usr/lib/libblas.dylib \
     /Developer/SDKs/MacOSX10.4u.sdk/usr/lib/liblapack.dylib

The resulting binary program can be run by typing ./simple_example

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