Procedure types & variables

  Use: procedure variables

• VAR proc:DoSomethingPr;        declaration
• proc := MyProc;            where MyProc is a defined procedure
• boolean := proc(4, integer);   procedure call
• NIL value: no procedure

Pointers

• variable declaration: VAR ptr: POINTER TO CARDINAL;
• assignment
• ptr := ptr2;
• NIL value: pointer points to nothing
• pointer value: ptr^
• ptr^ := 10;
• dynamic storage allocation:
• NEW(ptr);
• DISPOSE(ptr);  (ptr becomes NIL)
• pointer type: TYPE NodePt = POINTER TO NODE;  (* suffix Pt *)
• for pointers to structured types:
• TYPE ListArPt = POINTER TO ARRAY... (* suffix ArPt *)
•      PersonRcTp = POINTER TO RECORD ... (* suffix RcPt *)
• dynamics arrays (compile options M2EXTENSIONS and STORAGE must be set!)
• declare as an open array:
• TYPE ArrTp = ARRAY OF CARDINAL;
• VAR arr: POINTER TO ArrTp;
• multidimensional arrays:  TYPE ArrTp: ARRAY OF ARRAY OF CARDINAL;
• allocate
• NEW(arr, 10);
• multidimensional array: NEW(arr, 10, 5);
• use
• arr^[0] := 12;   (first element has index 0)
• arr^[9][4] := 12;
• deallocate (free the memory)
• DISPOSE(arr);

Libraries

The Definition Module

DEFINITION MODULE DemoLibrary;

  CONST
    STRING_MAX = 81;

  TYPE
    StringTp = ARRAY[0..STRING_MAX] OF CHAR;

  PROCEDURE StringLength(str: StringTp): CARDINAL;
                                 procedure heading only
                                 only open arrays or array types
  VAR
    errorMessage: StringTp;

END DemoLibrary.

The Implementation Module

IMPLEMENTATION MODULE DemoLibrary;

  PROCEDURE StringLength(str: StringTp): CARDINAL;
      ...
    BEGIN
      ...                          procedure implementation
  END StringLength;

BEGIN
  errorMessage := "no error until now";  initialisation of variables

END DemoLibrary.

Use

MODULE TestLibrary;

  FROM IO IMPORT WrStr, WrLn;     import procedures
  IMPORT DemoLibrary;            or import the whole module

  VAR
    str1: DemoLibrary.StringTp;   use

BEGIN
  WrStr(DemoLibrary.errorMessage);

END;

Use within XDS

• create DemoLibrary.def for definition module, DemoLibrary.mod for implementation module
• compile first the definition module, then the implementation module.
• put the 2 files in the same directory as the files where you want to use it

• create a lib file with the following command: XLIB /NEW DemoLibrary.lib DemoLibrary.obj (you find xlib under the bin folder)
• make it available within XDS:
• Add the lib file lib/x86 folder. 
• Add the sym file to the lib/x86 folder.
• Change the xc.tem file of your bin folder: add de following line under line  !"%s\n","import32"#"lib" 

  ! "%s\n","DemoLibrary"#"lib"

Compile options

• use: add <* OPTION + *> in the code directly after the first line MODULE ...
• see XDS help for a complete list (Compiler options and equations), the most important options are:
• <* WOFF + *> doesn't show compiler warnings
• <* NOOPTIMIZE + *> to prevent the compiler for optimising your code, because then you won't see all your code in the debugger
• <* M2EXTENSIONS + *>  and <* M2ADDTYPES + *>  for Modula-2 extensions as pointers, LONGCARD etc
• increase STACKLIMIT, HEAPLIMIT and GCTRESHOLD (eg. in the configuration file xc.cfg in XDS-directory/BIN) to allow your program to use more memory

Further (see Modula-2 book)

• other libraries
• read from/ write to file
• variant records
• opaque types (p 404): like void pointers in C
• WORD, ADDRESS
• SIZE() procedure