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Pascal Like Modula2
Volume Number:2
Issue Number:5
Column Tag:Pascal Procedures

Making Pascal Act Like Modula2

By Steve Rabalais, Rabalais Computing, Tempe, AZ

Seperate Compilation with TML Pascal

In order to develop large applications for the MacIntosh, it is desirable to have the capability to seperate your code into easily manageable pieces. This allows for modular programming and avoids having to compile all of your program each time which can be time consuming and frustrating for small changes. This article presents a procedure for doing this using the TML Pascal compiler.


The MDS linker (or Consulair's 'smart' linker) will take seperate 'REL' files containing the proper linkage information and combine them to create a stand alone application. What this procedure does is to describe the process of creating these 'REL' files. Basically, each module is a seperate Pascal program. The trick is to get the link files created properly so that the seperate modules will link together if one is changed and re-compiled.

Example Program

The example program below consists of three (3) seperate modules representing three segments of a single application. The first module (X_mod1.Pas) is the 'main' program. It contains the compiler directives necessary to create a 'LINK' text file for the LINKER. External references in segments are satisfied with:

1. Include statements for standard symbols and declarations. (ie. {$I quickdraw.ipas.}.)

2. Include statements for program globals (ie. {$I X_globals.ipas})

3. EXTERNAL procedure references.

The external references will allow the compiler to 'assume' the procedure exists and generate the appropriate temporary code. The actual addresses will be satisfied at link time.


The following scenario describes the compile/edit cycle for the example:

1. Compile X_mod1.Pas.

2 Compile X_mod2.Pas.

3. Compile X_mod3.Pas.

4. Link X_mod1.Link. (generated by X_mod1.Pas)

5. Run the application and discover a problem with X_mod2.Pas.

6. Edit X_mod2.Pas and compile 'only' X_mod2.Pas.

7. Link x_mod1.Link

8. Verify application runs properly.


These hints are a result of experience.

1. Occasionally an unidentified character will 'creep' into a text file which the compiler cannot recognize. The Pascal statement will look correct but the compiler will not accept it. To see the offending character, use the 'SHOW INVISIBLES' option in the MDS editor. It is usually a 'box looking' character. Just delete it.

2. Since the 'main' program module creates the LINKER file, you have to 'force' the compiler to generate the linker code for the runtime packages that are used in the other modules. (ie $PAS files). This is done by putting in a Pascal statement in the main program that will invoke a runtime package. Example .. 'Concat' will invoke the runtime package $PAS$Str package).


This procedure will allow you to create an application of essentially an unlimited size using the TML Pascal compiler. For large applications, this procedure is essential. It is good programming practice to plan ahead.

PROGRAM X_mod1(Input,Output);

{$I MemTypes.ipas}
{$I QuickDraw.ipas}
{$I OSIntf.ipas}
{$I ToolIntf.ipas}
{$I PackIntf.ipas}


{$I  X_globals.ipas}

{$U< X_mod2/Code}
{$U< X_mod3/Code}

PROCEDURE   P_mod1_proc1 (v_var1 : Str255) ; FORWARD;
 PROCEDURE P_mod2_proc1 (v_var1 : Str255) ; EXTERNAL;
 PROCEDURE P_mod3_proc1 (v_var1 : Str255) ; EXTERNAL;
PROCEDURE   P_mod1_proc2 (v_var1 : Str255) ; FORWARD; 

{== P_mod1_proc1 (v_var1 : Str255) ==}
PROCEDURE P_mod1_proc1;
  writeln (v_var1);
  writeln ('In P_mod1_proc1');

{== P_mod1_proc2 (v_var1 :Str255) ==}
PROCEDURE P_mod1_proc2;
  writeln (v_var1);
  writeln ('In P_mod1_proc2');

{== execution begins here ==}
  g_global1 := 000;
    P_mod1_proc1 ('From mod1_main');
    P_mod2_proc1 ('From mod1_main');
    P_mod3_proc1 ('From mod1_main');
    writeln      ('Type a 999 to quit, any other number to loop');
    Readln       (g_global1);
  UNTIL (g_global1 = 999);

PROGRAM X_mod2(Input,Output);

{$I MemTypes.ipas}
{$I QuickDraw.ipas}
{$I OSIntf.ipas}
{$I ToolIntf.ipas}
{$I PackIntf.ipas}

{$I X_globals.ipas}

PROCEDURE   P_mod2_proc1 (v_var1 : Str255); FORWARD ;
PROCEDURE   P_mod3_proc1 (v_var1 : Str255); EXTERNAL;
PROCEDURE   P_mod2_proc2 (v_var1 : Str255); FORWARD ;

{$S Code}
{== P_mod2_proc1 (v_var1 : Str255) ==}
PROCEDURE P_mod2_proc1;
  writeln (v_var1);
  writeln ('In P_mod2_proc1');

{== P_mod2_proc2 (v_var1 : Str255) ==}
PROCEDURE P_mod2_proc2;
  writeln (v_var1);
  writeln ('In P_mod2_proc2');

{$S main}
{== main ==}
  {-- Dummy main program --}

PROGRAM X_mod3(Input,Output);

{$I MemTypes.ipas}
{$I QuickDraw.ipas}
{$I OSIntf.ipas}
{$I ToolIntf.ipas}
{$I PackIntf.ipas}

{$I X_globals.ipas}

PROCEDURE     P_mod3_proc1 (v_var1 : Str255); FORWARD;
  PROCEDURE   P_mod1_proc1 (v_var1 : Str255); EXTERNAL;
  PROCEDURE   P_mod2_proc1 (v_var1 : Str255); EXTERNAL;
PROCEDURE     P_mod3_proc2 (v_var1 : Str255); FORWARD;

{$S Code}
{== P_mod3_proc1 (v_var1 : Str255) ==}
PROCEDURE P_mod3_proc1;
  writeln (v_var1);
  writeln ('In P_mod3_proc1');

{== P_mod3_proc2 (v_var1 : Str255) ==}
PROCEDURE P_mod3_proc2;
  writeln (v_var1);
  writeln ('In P_mod3_proc2');

{$S main}
{== main ==}
  {-- Dummy main program --}

{== application globals available to all segments ==}
  g_global1 : INTEGER ;
  g_global2 : Rect    ;
  g_global3 : LONGINT ;



/Type 'APPL' 'RABS'

Fig. 1 Combined program output


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