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# 2. Getting Started

This section outlines the ASIS application development and usage cycle. We first take a sample problem and present an ASIS application that offers a solution; then we show how to build the executable with ASIS-for-GNAT and how to prepare an ASIS "Context" to be processed by the program; and finally we show the output produced by our program when it is applied to itself.

> 2.1 The Problem |  |
> 2.2 An ASIS Application that Solves the Problem |  |
> 2.3 Required Sequence of Calls |  |
> 2.4 Building the Executable for an ASIS application |  |
> 2.5 Preparing Data for an ASIS Application - Generating Tree Files |  |
> 2.6 Running an ASIS Application |  |

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## 2.1 The Problem

We wish to process some set of Ada compilation units as follows: for every unit, print its full expanded Ada name, whether this unit is a spec(1), a body or a subunit, and whether this unit is a user-defined unit, an Ada predefined unit or an implementation-specific unit (such as a part of a Run-Time Library).

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## 2.2 An ASIS Application that Solves the Problem

    with Ada.Wide_Text_IO;        use Ada.Wide_Text_IO;
    with Ada.Characters.Handling; use Ada.Characters.Handling;

    --  ASIS-specific context clauses:
    with Asis;
    with Asis.Implementation;
    with Asis.Ada_Environments;
    with Asis.Compilation_Units;
    with Asis.Exceptions;
    with Asis.Errors;

    procedure Example1 is
       My_Context : Asis.Context;
       --  ASIS Context is an abstraction of an Ada compilation environment,
       --  it defines a set of ASIS Compilation Units available through
       --  ASIS queries

    begin
       --  first, by initializing an ASIS implementation, we make it
       --  ready for work
       Asis.Implementation.Initialize ("-ws");
       --  The "-ws" parameter of the Initialize procedure means
       --  "turn off all the ASIS warnings"

       --  then we define our Context by making an association with
       --  the "physical" environment:
       Asis.Ada_Environments.Associate
        (My_Context, "My Asis Context", "-CA");
       --  "-CA" as a Context parameter means "consider all the tree
       --  files in the current directory"
       --  See ASIS-for-GNAT Reference Manual for the description of the
       --  parameters of the Associate query, see also chapter
       --  "ASIS Context" for the description of different kinds of
       --  ASIS Context in case of ASIS-for-GNAT

       --  by opening a Context we make it ready for processing by ASIS
       --  queries
       Asis.Ada_Environments.Open (My_Context);

       Processing_Units: declare
          Next_Unit : Asis.Compilation_Unit;
          --  ASIS Compilation_Unit is the abstraction to represent Ada
          --  compilation units as described in RM 95

          All_Units : Asis.Compilation_Unit_List :=
          --  ASIS lists are one-dimensional unconstrained arrays.
          --  Therefore, when declaring an object of an ASIS list type,
          --  we have to provide either a constraint or explicit
          --  initialization expression:

             Asis.Compilation_Units.Compilation_Units (My_Context);
          --  The Compilation_Units query returns a list of all the units
          --  contained in an ASIS Context
       begin
          Put_Line
            ("A Context contains the following compilation units:");
          New_Line;
          for I in All_Units'Range loop
             Next_Unit := All_Units (I);
             Put ("   ");

             --  to get a unit name, we just need a Unit_Full_Name
             --  query. ASIS uses Wide_String as a string type,
             --  that is why we are using Ada.Wide_Text_IO

             Put (Asis.Compilation_Units.Unit_Full_Name (Next_Unit));

             --  to get more info about a unit, we ask about unit class
             --  and about unit origin

             case Asis.Compilation_Units.Unit_Kind (Next_Unit) is
                when Asis.A_Library_Unit_Body =>
                   Put (" (body)");
                when Asis.A_Subunit =>
                   Put (" (subunit)");
                when others =>
                   Put (" (spec)");
             end case;

             case Asis.Compilation_Units.Unit_Origin (Next_Unit) is
                when Asis.An_Application_Unit =>
                   Put_Line (" - user-defined unit");
                when Asis.An_Implementation_Unit =>
                   Put_Line (" - implementation-specific unit");
                when Asis.A_Predefined_Unit =>
                   Put_Line (" - Ada predefined unit");
                when Asis.Not_An_Origin =>
                   Put_Line
                     (" - unit does not actually exist in a Context");
             end case;

          end loop;
       end Processing_Units;

       --  Cleaning up: we have to close out the Context, break its
       --  association with the external environment and finalize
       --  our ASIS implementation to release all the resources used:
       Asis.Ada_Environments.Close (My_Context);
       Asis.Ada_Environments.Dissociate (My_Context);
       Asis.Implementation.Finalize;

    exception
       when Asis.Exceptions.ASIS_Inappropriate_Context |
            Asis.Exceptions.ASIS_Inappropriate_Compilation_Unit |
            Asis.Exceptions.ASIS_Failed =>

          --  we check not for all the ASIS-defined exceptions, but only
          --  those of them which can actually be raised in our ASIS
          --  application.
          --
          --  If an ASIS exception is raised, we output the ASIS error
          --  status and the ASIS diagnosis string:

          Put_Line ("ASIS exception is raised:");
          Put_Line ("ASIS diagnosis is:");
          Put_Line (Asis.Implementation.Diagnosis);
          Put      ("ASIS error status is: ");
          Put_Line
            (Asis.Errors.Error_Kinds'Wide_Image
               (Asis.Implementation.Status));
    end Example1;

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## 2.3 Required Sequence of Calls

An ASIS application must use the following sequence of calls:

1. `Asis.Implementation.Initialize (...);`

   This initializes the ASIS implementation's internal data structures. In general, calling an ASIS query is erroneous unless the `Initialize` procedure has been invoked.

2. `Asis.Ada_Environments.Associate (...);`

   This call is the only means to define a value of a variable of the ASIS limited private type `Context`. The value represents some specific association of the ASIS `Context` with the "external world". The way of making this association and the meaning of the corresponding parameters of the `Associate` query are implementation-specific, but as soon as this association has been made and a `Context` variable is opened, the ASIS `Context` designated by this variable may be considered to be a set of ASIS `Compilation_Unit`s available through the ASIS queries.

3. `Asis.Ada_Environments.Open (...);`

   Opening an ASIS `Context` variable makes the corresponding `Context` accessible to all ASIS queries.

   After opening the `Context`, an ASIS application can start obtaining ASIS `Compilation_Unit`s from it, can further analyze `Compilation_Unit`s by decomposing them into ASIS `Element`s, etc.

   ASIS relies on the fact that the content of a `Context` remains "frozen" as long as the `Context` remains open. It is erroneous to change through some non-ASIS program any data structures used by an ASIS implementation to define and implement this `Context` while the `Context` is open.

4. Now all the ASIS queries can be used. It is possible to access `Compilation_Unit`s from the `Context`, to decompose units into syntactic `Element`s, to query syntactic and semantic properties of these `Element`s and so on.

5. `Asis.Ada_Environments.Close (...);`

   After closing the `Context` it is impossible to retrieve any information from it. All the values of the ASIS objects of `Compilation_Unit`, `Element` and `Line` types obtained when this `Context` was open become obsolete, and it is erroneous to use them after the `Context` was closed. The content of this `Context` need not be frozen while the `Context` remains closed. Note that a closed `Context` keeps its association with the "external world" and it may be opened again with the same association. Note also that the content (that is, the corresponding set of ASIS `Compilation_Unit`s) of the `Context` may be different from what was in the `Context` before, because the "external world" may have changed while the `Context` remained closed.

6. `Asis.Ada_Environments.Dissociate (...);`

   This query breaks the association between the corresponding ASIS `Context` and the "external world", and the corresponding `Context` variable becomes undefined.

7. `Asis.Implementation.Finalize (...);`

   This releases all the resources used by an ASIS implementation.

An application can perform these steps in a loop. It may initialize and finalize an ASIS implementation several times, it may associate and dissociate the same `Context` several times while an ASIS implementation remains initialized, and it may open and close the same `Context` several times while the `Context` keeps its association with the "external world".

An application can have several ASIS `Context`s opened at a time (the upper limit is implementation-specific), and for each open `Context`, an application can process several `Compilation_Unit`s obtained from this `Context` at a time (the upper limit is also implementation-specific). ASIS-for-GNAT does not impose any special limitations on the number of ASIS `Context`s and on the number of the ASIS `Compilation_Unit`s processed at a time, as long as an ASIS application is within the general resource limitations of the underlying system.

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## 2.4 Building the Executable for an ASIS application

The rest of this section assumes that you have ASIS-for-GNAT properly installed as an Ada library.

To get the executable for the ASIS application from 2.2 An ASIS Application that Solves the Problem (assuming that it is located in your current directory as the Ada source file named ``example1.adb'`), invoke `gnatmake` as follows(2):

    $ gnatmake example1.adb -largs -lasis

For more details concerning compiling ASIS applications and building executables for them with ASIS-for-GNAT see 10. Compiling, Binding and Linking Applications with ASIS-for-GNAT.

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## 2.5 Preparing Data for an ASIS Application - Generating Tree Files

The general ASIS implementation technique is to use some information generated by the underlying Ada compiler as the basis for retrieving information from the Ada environment. As a consequence, an ASIS application can process only legal (compilable) Ada code, and in most of the cases to make a compilation unit "visible" for ASIS means to compile this unit (probably with some ASIS-specific options)

ASIS-for-GNAT uses tree output files (or, in short, tree files) to capture information about an Ada unit from an Ada environment. A tree file is generated by GNAT, and it contains a snapshot of the compiler's internal data structures at the end of the successful compilation of the corresponding source file.

To create a tree file for a unit contained in some source file, you should compile this file with the ``-gnatct'` compiler option. If you want to apply the program described in section 2.2 An ASIS Application that Solves the Problem to itself, compile the source of this application with the command:

    $ gcc -c -gnatct example1.adb

and as a result, GNAT will generate the tree file named ``example1.adt'` in the current directory.

For more information on how to generate and deal with tree files, see 4. ASIS `Context`, and 7. ASIS Tutorials.

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## 2.6 Running an ASIS Application

To complete our example, let's execute our ASIS application. If you have followed all the steps described in this chapter, your current directory should contain the executable ``example1'` (``example1.exe'` on a Windows platform) and the tree file ``example1.adt'`. If we run our application, it will process an ASIS `Context` defined by one tree file ``example1.adt'` (for more details about defining an ASIS `Context` see 4. ASIS `Context`, and the ASIS-for-GNAT Reference Manual). The result will be:

       A Context contains the following compilation units:

          Standard (spec) - Ada predefined unit
          Example1 (body) - user-defined unit
          Ada (spec) - Ada predefined unit
          Ada.Wide_Text_IO (spec) - Ada predefined unit
          Ada.IO_Exceptions (spec) - Ada predefined unit
          Ada.Streams (spec) - Ada predefined unit
          System (spec) - Ada predefined unit
          System.File_Control_Block (spec) - implementation-specific unit
          Interfaces (spec) - Ada predefined unit
          Interfaces.C_Streams (spec) - implementation-specific unit
          System.Parameters (spec) - implementation-specific unit
          System.WCh_Con (spec) - implementation-specific unit
          Ada.Characters (spec) - Ada predefined unit
          Ada.Characters.Handling (spec) - Ada predefined unit
          Asis (spec) - user-defined unit
          A4G (spec) - user-defined unit
          A4G.A_Types (spec) - user-defined unit
          Ada.Characters.Latin_1 (spec) - Ada predefined unit
          GNAT (spec) - implementation-specific unit
          GNAT.OS_Lib (spec) - implementation-specific unit
          GNAT.Strings (spec) - implementation-specific unit
          Unchecked_Deallocation (spec) - Ada predefined unit
          Sinfo (spec) - user-defined unit
          Types (spec) - user-defined unit
          Uintp (spec) - user-defined unit
          Alloc (spec) - user-defined unit
          Table (spec) - user-defined unit
          Urealp (spec) - user-defined unit
          A4G.Int_Knds (spec) - user-defined unit
          Asis.Implementation (spec) - user-defined unit
          Asis.Errors (spec) - user-defined unit
          Asis.Ada_Environments (spec) - user-defined unit
          Asis.Compilation_Units (spec) - user-defined unit
          Asis.Ada_Environments.Containers (spec) - user-defined unit
          Asis.Exceptions (spec) - user-defined unit
          System.Unsigned_Types (spec) - implementation-specific unit

Note that the tree file contains the full syntactic and semantic information not only about the unit compiled by the given call to `gcc`, but also about all the units upon which this unit depends semantically; that is why you can see in the output list a number of units which are not mentioned in our example.

In the current version of ASIS-for-GNAT, ASIS implementation components are considered user-defined, rather than implementation-specific, units.

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