PROGRAM

The program header is not required, it is provided only for backward compatibility with Turbo Pascal.

   program name [(parameters, ...)] [: address];

It is possible to specify the compilation address after the colon character :, this is equivalent to the command-line switch -code address.

program test;

uses // List of unit dependencies goes here...

// Implementation of procedures, and functions goes here...

end.

UNIT

The UNIT modules come only in the form of source .pas files, they cannot be compiled separately.

The UNIT modules consist of sections:

• INTERFACE wymagana
• IMPLEMENTATION wymagana
• INITIALIZATION opcjonalna.

{
  Example UNIT
}
unit Unit1;

interface

uses // List of unit dependencies goes here...

// Interface section goes here

implementation

uses // List of unit dependencies goes here...

// Implementation of procedures, and functions goes here...

initialization

// Unit initialization code goes here...

end.

Example:

unit test;

interface

type  TUInt24 =
  record
    byte0: byte;
    byte1: byte;
    byte2: byte;
  end;

const
  LoRes = 1;
  MedRes = 2;
  HiRes = 3;

  procedure Print(a: string);

implementation

uses test2;

procedure Print(a: string);
begin

  writeln(a);

end;

end.

LIBRARY

The library header is required.

   library name [: address];

It is possible to specify the compilation address after the colon character :, this is equivalent to the command-line switch -code address.

The structure of the library is similar to the unit module, program program.

{
  Example LIBRARY
}
library lib1;

uses // List of unit dependencies goes here...

// Implementation of procedures, and functions goes here...


// exported subroutine(s), variable(s)

exports

idents, ... ;

// optional library initialization code goes here...

begin

end.

By default, functions and procedures declared and implemented in the library are not available to a programmer who wants to use the library.

To make functions or procedures from the library available, they must be exported in the exports clause.

Functions, procedures and other identifiers are exported with the exact names specified in the exports clause.

To use libraries in UNIT modules or PROGRAM program, they must first be compiled and assembled, the Mad Assembler-a -hm switch must be active.

mads.exe library.pas -hm -xi:<Mad_Pascal_path>\base

We cannot place .pas files with library source code in the uses clause.

To use the identifiers exported in LIBRARY we use the EXTERNAL modifier.

USES

The uses clause imports identifiers from unit modules.

Each Mad-Pascal unit - program, unit, or library - can have a maximum of one uses clause per section, which must appear immediately after the section headers.

Section headers are interface, implementation in unit modules. There are no explicit section headers in program and library, so the uses clause appears immediately after the program, library header.

    uses crt, sysutils, atari;

The SYSTEM module cannot be in this list, because it is always loaded by the compiler by default.

The order in which modules appear is important because it determines the order in which they are initialized. Modules are initialized in the same order in which they appear in the uses clause.

Identifiers are searched for in reverse order, that is, when the compiler looks for an identifier, it looks for it first in the last module in the uses clause, then in the penultimate one, and so on. This is important when two or more modules in the uses clause declare the same identifier.

uses graph, vbxe;

In both GRAPH and VBXE modules there is a SetColor and Line procedure, for the aforementioned example references to these procedures will be made by the VBXE module,

uses vbxe, graph;

references to these procedures will be made by the GRAPH module.

We can also directly refer to the identifier from a specific module, such as:

    vbxe.Line
    graph.Line
    vbxe.SetColor
    graph.SetColor

The compiler will look for source versions of all modules listed in the uses clause based on the path from which the mp.exe compiler was run.

Using the IN keyword, we can override the automatic module search mechanism.

    uses unita in '..\unita.pas';

The unita module is searched for in the parent directory of the current compiler working directory. You can add a {$UNITPATH ..} directive to ensure that the module is found no matter where the current compiler working directory is.

When the compiler looks for module files, it adds the .pas extension to the module name.

$LIBRARYPATH

{$LIBRARYPATH path1; path2; ...}

The $LIBRARYPATH directive allows you to indicate additional search paths for UNIT modules declared by uses.

$UNITPATH

{$UNITPATH path1; path2; ...}

The $UNITPATH directive allows you to indicate additional search paths for UNIT modules declared by uses.