The Programming Language

1
The Programming Language

• By Doug Bell, Ian Morrey
• and
• John Pugh

2
Introduction

• Discusses the features that a good programming
  language should have from the viewpoint of the SW
  engineer such as FORTRAN, COBOL, C, Pascal, and
  Ada what features encourage the development of
  software that is reliable, maintainable and
  efficient
• Programming languages are very difficult to
  evaluate and compare
• COBOL- Data processing community
• FORTRAN - language of scientist and engineer
• Ada- real time or embedded computer systems
• C- Systems programmer

3
Classification of programming Languages

• High-level, Low-level, Systems implementation
  language or high-level assembler
• weakly or strongly typed
• compiled or interpreted

4
Selection of programming language

• Many organizations have a substantial investment
  in a particular programming language
• Contact that actually specifies the programming
  language
• Support from suppliers of major software
  components, compilers and database management
  systems
• Language sensitive editors,debugging systems,
  project management tools and development tools

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Programming in the small

• 1. Simplicity, Clarity and Orthogonality
• SimpleLarger no.of features more complex
• Clarity There is design languages for the
  programmers than for the machines
• high-level languages
• natural, unambiguous and meaningful
• Orthogonality possible to combine language
  features freely special cases and restrictions
  should not be prevalent

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Programming in the small

• 2. Language Syntax consistent, natural, and
  promote readability of programs
• A number of systematic concepts help the physical
  layout of a program to reflect dynamic algorithm
• The readability of program improved by the use of
  meaningful identifiers and consistency of
  language syntax

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Programming in the small

• 3.Control Abstractions small but powerful set of
  control structures to describe the flow of
  execution within a program unit
• Basic structured programming constructs
  Sequence, Selection(IF,CASE) and
  Repetition(iterations fixed, controlled by
  evaluation of some conditions)
• Basic set of primitives fits in well with the
  top-down philosophy of program design
• Each primitive has a single entry and exit points

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Programming in the small

• 4.Data Types and Strong Typing Data type is a
  set of data objects and operations applicable to
  all objects of that type and a language said to
  be Strongly typed if it can be determined at
  compile-time whether or not each operation
  performed on an object is consistent with the
  type of that object
• Strongly typed languages are more clear, reliable
  and portable
• dynamic (change at run-time) and static typing

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Programming in the small

• 4.Data Types and Strong Typing(cont)
• a. Primitive Data Types Boolean, Character,
  Integer,Real, supporting cast of operations,
  literals or constants
• Pointer data type Provide the ability to refer
  to data object indirectly eg lists and trees
• Arrays Mapping is less clear and less flexible
• Readability, reliability, data abstraction
  capabilities are enhanced if the programmer
  extend the primitive data types

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Programming in the small

• 4.Data Types and Strong Typing(cont)
• b. Structured data types
• Arrays homogeneous elements
• Record in FORTRAN heterogeneous elements
• Variant records or discriminated unions union of
  several subtypes based on some discriminating tag
  field

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Programming in the small

• 4.Data Types and Strong Typing(cont)
• c. Strong Vs Weak Typing Strong typing will be
  seen as most desirable but languages must provide
  well defined escape mechanisms to circumvent type
  checking
• implicit and explicit conversions

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Programming in the small

• 5. Procedural Abstraction what should be done
  before how it should be done
• Procedures and functions allow layered design and
  factoring increases readability and
  maintainability of program
• Procedures should only accept and return
  information through their parameters and
  functions should accept but not return
• Recursion Cobol, Fortran does not support

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Programming in the small

• 5. Procedural Abstraction (cont)
• a. Parameter Passing Mechanism
• Input, output, Input-output parameters
• Fortran parameter passing mode call by
  reference in input-output parameters- Location
  of actual parameter is bound to the formal
  parameter
• Pascal uses both call by reference in both
  input-output, output parameters and call by
  value in input parameters
• ADA uses in, out, and in out

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Programming in the small

• 5. Procedural Abstraction (cont)
• a. Scoping Mechanisms
• Objects used within the procedure should have no
  effect outside the procedure
• Information hiding
• Scope to control the visibility of names
• BASIC- provides no scoping-global variable
• Fortran- sub routine or function- local variable
• Algol, Pascal, and ADA are block-structured
  languages

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Programming in the large

• Undergo continual maintenance and enhancement
  over extended lifetime
• Integrate the software tools with particular
  language to form integrated software environment
  Ex Ada Programming Support Environment (APSE)
• Functional, Data Abstractions
• Use of abstractions provides modularity, reuse of
  code and information hiding
• Interface between modules must be carefully
  controlled
• Strong type checking across module boundaries

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Programming in the large

• 1.Functional and data Abstractions
• Functional Abstraction in the form of procedures
  or functions
• An abstract data type consists of a set of
  objects and operations
• Programming language should include
  Encapsulation, clear separation between
  specification and implementation of abstraction,
  Information hiding, reusable program modules

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Programming in the large

• 1.Functional and data Abstractions (cont)
• In Pascal, functional abstraction at the level of
  procedure or function and provide support for
  transparent data types and gives little support
  for data abstraction
• Ada provides encapsulation mechanisms at
  subprogram and package level- Two parts of
  package, specification and body which are
  separately compiled
• Generics allow programmers to define templates
  for packages and procedures

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Programming in the large

• 2.Seperate Compilation
• Integration of routines that have been developed
  separately
• Additional support environmental tools such as
  linkers, cross reference generators, file
  librarians, and source code control systems
• Fortran provides independent compilation of
  modules at sub routine level but no run-time
  checking of calls to external routines
• Pascal provides no support for separate
  compilation and Ada provides greater support for
  separate compilation with strong type checking