Modula 2 tutorial - 003 - declarations
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This document provides an overview of declarations in the Modula-2 programming language. It discusses the rules for declaring constants, types, variables, procedures, and modules. Constants are assigned values at compile time and cannot change during execution. Types define the set of values variables can assume and their structure. Variables are allocated memory of a specified type. Procedures and functions are declared with a heading specifying their identifier and parameters, and a block containing statements.
![Types declaration
TYPE
Integer = INTEGER;
SmallInt = [-10..10];
Color = (Red, Green, Blue);
CharPointer = POINTER TO CHAR;
ColorSet = SET OF COLOR;
String = ARRAY [0..255] OF CHAR;
Integer type
Pointer type
Set type
Array type
Subrange type
Enumeration type
A data type determines a set of values which variables of that type may assume, and it associates an identifier with the type.
In the case of structured types, it also defines the structure of variables of this type. There are three different structures, namely
arrays, records, and sets. Standard types are: INTEGER, CARDINAL, BOOLEAN, REAL, CHAR, POINTER.
There are other useful types exported by the module SYSTEM that specified the machine size such as CARD16, INT16, CARD32,
INT32, BYTE, WORD and others.
Julian Miglio 2019
Complex = RECORD A,B : REAL; END;
RealFunc = PROCEDURE(REAL) : REAL;
Record (structure) type
Procedure type](https://image.slidesharecdn.com/modula-2tutorial-003-declarations-191019144254/85/Modula-2-tutorial-003-declarations-4-320.jpg)
![Variables declaration
VAR
I, J : INTEGER;
MAT : ARRAY [1..3],[1..3] OF REAL;
BackGround, ForeGround : Color;
PossibleColors : SET OF Color;
RecordPointer : POINTER TO RecType;
Integer variable
Set variable
Pointer to record variable
Array variable
Enumeration variable
Variable declaration is the definition and allocation of memory of a particular type. The data type determines the set of values
that a variable may assume and the operators that are applicable to it, it also defines the structure of the variable.
Each of the identifiers to the left of the colon is declared as a variable of the type that is specified to the right of the colon.
Julian Miglio 2019](https://image.slidesharecdn.com/modula-2tutorial-003-declarations-191019144254/85/Modula-2-tutorial-003-declarations-5-320.jpg)
Modula 2 tutorial - 003 - declarations
- 1. Modula-2 ISO/IEC 10514 programming language tutorial Declarations Julian Miglio 2019
- 2. Declarations rules IMPLEMENTATION MODULE MyModule; CONST TYPE VAR Constants declaration Types declaration Variables declaration PROCEDURE MyProc; CONST TYPE VAR Constants declaration Types declaration Variables declaration Every identifier occurring in a program must be introduced by a declaration, unless it is a standard identifier. Declarations also specify certain permanent properties of an object, such as whether it is a constant, a type, a variable, a procedure, or a module. The identifier is then used to refer to the associated object. Julian Miglio 2019 BEGIN END MyModule. Procedures declaration BEGIN END MyProc; Procedures declaration
- 3. Constants declaration CONST One = 1; Pi = 3.14159; PiOver2 = Pi / 2.0; Debug = TRUE; Integer constant Floating point constant Floating point constant Boolean constant Constants are objects that have a specific value assigned at compile time. Constants cannot change during the execution of the program. For simple types, value is an expression giving the value of the constant. The expression must be made up of constants only, so that the compiler can evaluate it at compile time. It is also possible declare constants of array and record types. Julian Miglio 2019 Debug = TRUE; Message = "That's not right!"; Boolean constant String constant
- 4. Types declaration TYPE Integer = INTEGER; SmallInt = [-10..10]; Color = (Red, Green, Blue); CharPointer = POINTER TO CHAR; ColorSet = SET OF COLOR; String = ARRAY [0..255] OF CHAR; Integer type Pointer type Set type Array type Subrange type Enumeration type A data type determines a set of values which variables of that type may assume, and it associates an identifier with the type. In the case of structured types, it also defines the structure of variables of this type. There are three different structures, namely arrays, records, and sets. Standard types are: INTEGER, CARDINAL, BOOLEAN, REAL, CHAR, POINTER. There are other useful types exported by the module SYSTEM that specified the machine size such as CARD16, INT16, CARD32, INT32, BYTE, WORD and others. Julian Miglio 2019 Complex = RECORD A,B : REAL; END; RealFunc = PROCEDURE(REAL) : REAL; Record (structure) type Procedure type
- 5. Variables declaration VAR I, J : INTEGER; MAT : ARRAY [1..3],[1..3] OF REAL; BackGround, ForeGround : Color; PossibleColors : SET OF Color; RecordPointer : POINTER TO RecType; Integer variable Set variable Pointer to record variable Array variable Enumeration variable Variable declaration is the definition and allocation of memory of a particular type. The data type determines the set of values that a variable may assume and the operators that are applicable to it, it also defines the structure of the variable. Each of the identifiers to the left of the colon is declared as a variable of the type that is specified to the right of the colon. Julian Miglio 2019
- 6. Procedures and functions declaration PROCEDURE Error; BEGIN WriteString('ERROR'); END Error; PROCEDURE tan(x : REAL) : REAL; BEGIN RETURN sin(x) / cos(x); END tan; Function with an input parameter and a return parameter Procedure without parameters Procedure declarations consist of a procedure heading and a block. The heading specifies the identifier and the formal parameters, the block contains other declarations and executable statements. There are two kinds of procedures: procedures and functions. The first is activated by a procedure call, while the second is called in an expression and returns a value. Procedures are sequences of instructions that perform a specific task. Usually, procedures are used when the same sequence of code is required more than once in a program. In this case, the procedure is written once and is called from several places. Julian Miglio 2019 PROCEDURE tan(x : REAL) : REAL; FORWARD; Forward declaration
- 7. Reference • Modula-2: Abstractions for Data and Programming Structures: http://www.arjay.bc.ca/Modula-2/Text/index.html • ISO/IEC 10514 Modula-2, Base Language: https://www.iso.org/standard/18583.html • Modula2.org: https://www.modula2.org/ Julian Miglio 2019 • Modula2.org: https://www.modula2.org/