Modula2

1
Modula-2

• From design and development to uses and
  performance
• Dmitry Nesvizhsky
• CIS24
• Professor Danny Kopec

2
Design and Development

• Modula-2 was developed by
  Niklaus Wirth at ETH in Zurich,
  Switzerland in the late 70's
• Wirth focused on building a single language for a
  new computer system that was later called Lilith

3
Design and Development

• Modula-2
• Procedural Programming Language
• Block-structured
• Design was based on Pascal and Modula
• Improvements over Pascal
• Modules
• Low-level features
• Coroutines
• Syntactic features

4
Design and Development

• Modules
• A tool for expressing the relations between major
  parts of programs and provide support for
  abstract data types
• Low-Level Features
• a small language, which can be implemented on a
  wide variety of microcomputers
• Contains facilities for high-level and low-level
  programming

5
Design and Development

• Coroutines
• Used for embedded systems that require
  concurrency without the overhead of large
  operating systems or large languages
• Syntactic Features
• Have a small vocabulary and consists of few
  sentence structures
• Contains simple and consistent rules of syntax,
  which makes it easy to learn

6
Superiority of Modula-2

• Supports Modular design
• Reduces errors and cuts down on maintenance time
• Allows platform dependencies to be isolated
• Increases portability
• I/O code is smaller and faster than the
  resource-hungry printf in C

7
Superiority of Modula-2

• Modula-2 is a higher-level language than C
• E.g. with respect to pointers
• Pointers have types that depend on what is
  pointed to
• Modula-2 treats these as addresses only by
  flagging this fact in the code
• Identifiers are case sensitive
• No GOTO label

8
Uses of Modula-2

• Suitable for learning programming
• Large projects written and maintained in the
  fashion of professional software engineers
• real-time embedded systems
• Safety-critical areas
• Traffic control systems
• It is small, expressive, easy to learn, and to
  read

9
Code Example 1

• The program prints Hello World! to the screen
• MODULE PrintHelloWorld
• (This program prints "Hello world!" on the
  standard output device)
• FROM InOut IMPORT WriteString, WriteLn
• BEGIN
• WriteString('Hello world!')
• WriteLn
• END PrintHelloWorld.

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Code Example 2

• Given the names of the input and output files,
  the following program reads the numbers from the
  input file and outputs the sum and average into
  the output file

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Code Example 2 (continued)

• MODULE SumAndAverage
• FROM InOut IMPORT ReadInt, WriteString, WriteLn,
  WriteInt, OpenInput, OpenOutput, CloseInput,
  CloseOutput, Done
• VAR 
• NINTEGER
• XINTEGER
• SUMINTEGER
• AVERAGEINTEGER

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Code Example 2 (continued)

• BEGIN
• WriteString('Enter the names of the output,
  input files')
• WriteLn
• OpenOutput("OUT")
• IF NOT Done THEN
• WriteString('Output file cannot be opened')
• WriteLn
• HALT
• END
• OpenInput("IN")
• IF NOT Done THEN
• CloseOutput
• WriteString('Input file cannot be opened')
• WriteLn
• HALT
• END

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Code Example 2 (continued)

• N0
• SUM0
• ReadInt(X)
• WHILE Done DO
• WriteInt(X,3)
• WriteLn
• NN1
• SUMSUMX
• ReadInt(X)
• END

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Code Example 2 (continued)

• WriteString('The Sum is ')
• WriteInt(SUM,1)
• WriteLn
• AVERAGESUM DIV N
• WriteString('The Average is')
• WriteInt(AVERAGE,1)
• WriteLn
• CloseOutput
• CloseInput
• END SumAndAverage.

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Modula-2 Performance Table