6. ASIS Interpreter asistant

This chapter describes asistant, an interactive interface to ASIS queries.

6.1. asistant Introduction

The asistant tool allows you to use ASIS without building your own ASIS applications. It provides a simple command language that allows you to define variables of ASIS types and to assign them values by calling ASIS queries.

This tool may be very useful while you are learning ASIS: it lets you try different ASIS queries and see the results immediately. It does not crash when there is an error in calling an ASIS query (such as passing an inappropriate Element); instead asistant reports an error and lets you try again.

You can also use asistant as a debug and ‘ASIS visualization’ tool in an ASIS application project. If you have problems finding out which query should be used in a given situation, or why a given query does not work correctly with a given piece of Ada code, you may use asistant to reconstruct the situation that causes the problems, and then experiment with ASIS queries.

Though primarily an interactive tool, asistant also can interpret sequences of commands written to a file (called a ‘script file’ below). The asistant tool can also store in a file the log of an interactive session that can then be reused as a script file.

The full documentation of asistant may be found in the asistant Users’ Guide (file asistant.ug in the asistant source directory). Here is a brief overview of asistant usage.

The executable for asistant is created in the asistant source directory as a part of the standard procedure of installing ASIS-for-GNAT as an Ada library (or it is placed in the GNATPRO/bin directory when installing ASIS from the binary distribution). Put this executable somewhere on your path (unless you have installed ASIS from the binary distribution, in which case the executable for asistant has been added to other GNAT executables). Then type ‘asistant’ to call asistant in an interactive mode. As a result, the program will output brief information about itself and then the asistant prompt ‘>’ will appear:

ASIStant - ASIS Tester And iNTerpreter, v1.2
(C) 1997-2002, Free Software Foundation, Inc.
  Asis Version: ASIS 2.0.R


Now you can input asistant commands (asistant supports in its command language the same form of comments as Ada, and names in asistant are not case-sensitive):

>Initialize ("") -- the ASIS Initialize query is called with an
                 -- empty string as a parameter

>set (Cont) --  the non-initialized variable Cont of the ASIS
            --  Context type is created

>Associate (Cont, "", "") --  the ASIS Associate query with two empty
                          --  strings as parameters is called for Cont

>Open (Cont)  --  the ASIS Open query is called for Cont

>set (C_U, Compilation_Unit_Body ("Test", Cont)) -- the variable C_U
  --  of the ASIS Compilation_Unit type is created and initialized as
  --  the result of the call to the ASIS query Compilation_Unit_Body.
  --  As a result, C_U will represent a compilation unit named "Test"
  --  and contained in the ASIS Context named Cont

>set (Unit, Unit_Declaration (C_U))  --  the variable Unit of the ASIS
  --  Element type is created and initialized as the result of calling
  --  the ASIS Unit_Declaration query

>print (Unit) --  as a result of this command, some information about
              --  the current value of Unit will be printed (a user can set
              --  the desired level of detail of this information):

A_PROCEDURE_BODY_DECLARATION at ( 1 : 1 )-( 9 : 9 )

--  suppose now, that we do make an error - we call an ASIS query for
--  an inappropriate element:

>set (Elem, Assignment_Expression (Unit))

--  ASIS will raise an exception, asistant will output the ASIS debug
--  information:

Exception is raised by ASIS query ASSIGNMENT_EXPRESSION.
Diagnosis :
Inappropriate Element Kind in Asis.Statements.Assignment_Expression

--  it does not change any of the existing variables and it prompts
--  a user again:

> ...

6.2. asistant commands

The list of asistant commands given in this section is incomplete; its purpose is only to give a general idea of asistant’s capabilities. Standard metalanguage is assumed (i.e., ‘[construct]’ denotes an optional instance of ‘construct’).

Help [(name)]

Outputs the profile of the ASIS query ‘name’; when called with no argument, generates general asistant help information.

Set (name)

Creates a (non-initialized) variable ‘name’ of the ASIS Context type.

Set (name, expr)

Evaluates the expression ‘expr’ (it may be any legal asistant expression; a call to some ASIS query is the most common case in practice) and creates the variable ‘name’ of the type and with the value of ‘expr’.

Print (expr)

Evaluates the expression ‘expr’ and outputs its value (some information may be omitted depending on the level specified by the PrintDetail command).

Run (filename)

Launches the script from a file filename, reading further commands from it.


Pauses the current script and turns asistant into interactive mode.


Resumes a previously Paused script.


Switches asistant into step-by-step ASIS tree browsing.

Log (filename)

Opens the file filename for session logging.


Closes the current log file.


Toggles whether the Print command outputs additional information.

Quit [(exit-status)]

Quits asistant.

6.3. asistant variables

The asistant tool lets you define variables with Ada-style (simple) names. Variables can be of any ASIS type and of conventional Integer, Boolean and String type. All the variables are created and assigned dynamically by the Set command; there are no predefined variables.

There is no type checking in asistant: each call to a Set command may be considered as creating the first argument from scratch and initializing it by the value provided by the second argument.

6.4. Browsing an ASIS tree

You perform ASIS tree browsing by invoking the asistant service function Browse. This will disable the asistant command interpreter and activate the Browser command interpreter. The Browser Q command switches back into the asistant environment by enabling the asistant command interpreter and disabling the Browser interpreter.

Browse has a single parameter of Element type, which establishes where the ASIS tree browsing will begin. Browse returns a result of type Element, namely the Element at which the tree browsing was stopped. Thus, if you type:

> set (e0, Browse (e1))

you will start ASIS tree browsing from e1; when you finish browsing, e0 will represent the last Element visited during the browsing.

If you type:

> Browse (e1)

you will be able to browse the ASIS tree, but the last Element of the browsing will be discarded.

Browser displays the ASIS Element it currently points at and expects one of the following commands:


Go one step up the ASIS tree (equivalent to calling the ASIS Enclosing_Element query);


Go one step down the ASIS tree, to the left-most component of the current Element


Go to the right sibling (to the next Element in the ASIS tree hierarchy)


Go to the left sibling (to the previous Element in the ASIS tree hierarchy)


where k1 is either D or d, and k2 is either T or t. Change the form of displaying the current Element: D turns ON displaying the debug image, d turns it OFF. T turns ON displaying the text image, t turns it OFF.


Call the <query> for the current Element.


Go back to the asistant environment; the Browser command interpreter is disabled and the asistant command interpreter is enabled with the current Element returned as a result of the call to Browse.

Browser immediately interprets the keystroke and displays the new current Element. If the message "Cannot go in this direction." appears, this means that traversal in this direction from current node is impossible (that is, the current node is either a terminal Element and it is not possible to go down, or it is the leftmost or the rightmost component of some Element, and it is not possible to go left or right, or it is the top Element in its enclosing unit structure and it is not possible to go up).

It is possible to issue some ordinary ASIS queries from inside the Browser (for example, semantic queries). These queries should accept one parameter of type Element and return Element as a result.

When you press <SPACE>, you are asked to enter the query name. If the query is legal, the current Element is replaced by the result of the call to the given query with the current Element as a parameter.

6.5. Example

Suppose we have an ASIS Compilation_Unit Demo in the source file demo.adb:

procedure Demo is
   function F (I : Integer) return Integer;

   function F (I : Integer) return Integer is
      return (I + 1);
   end F;

   N : Integer;

    N := F (3);
end Demo;

Suppose also that the tree for this source is created in the current directory. Below is a sequence of asistant commands which does process this unit. Explanation is provided via asistant comments.

initialize ("")

--  Create and open a Context comprising all the tree files
--  in the current directory:

Set (Cont)
Associate (Cont, "", "")
Open (Cont)

-- Get a Compilation_Unit (body) named "Demo" from this Context:

Set (CU, Compilation_Unit_Body ("Demo", Cont))

--  Go into the unit structure and get to the expression
--  in the right part of the assignment statements in the unit body:

Set (Unit, Unit_Declaration (CU))
Set (Stmts, Body_Statements (Unit, False))
Set (Stmt, Stmts (1))
Set (Expr, Assignment_Expression (Stmt))

-- Output the debug image and the text image of this expression:

Print (Expr)
Print (Element_Image (Expr))

--  This expression is of A_Function_Call kind, so it's possible to ask
--  for the declaration of the called function:

Set (Corr_Called_Fun, Corresponding_Called_Function (Expr))

--  Print the debug and the text image of the declaration of the called
--  function:

Print (Corr_Called_Fun)
Print (Element_Image (Corr_Called_Fun))

-- Close the asistant session: