CS 322 Programming Language Concepts

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CS 322Programming Language Concepts
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Logistics

• All handouts will be kept on-line
• Course Home Page
• http//csce.unl.edu/samal/class/FALL/f06/322/322.
  htm

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Study programming languages Why?

• Use of existing languages
• Vocabulary of useful programming constructs
• Better choice of programming languages
• Ease of learning new languages
• Ease of designing new languages
• Develop effective algorithms

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Study programming languages How?

• Grand Tour
• Learn different languages, C, C, Java, Lisp,
  etc.
• Languages become obsolete and new languages are
  designed all the time.
• Principles
• Learn the underlying principles, vocabulary,
  structure and meaning
• More enduring

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If you give a man a fish he will have a single
meal. If you teach him how to fish, he will eat
all his life. Kuan-tzu (Chinese Philosopher)
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Design Principles

• Syntax
• What is a correctly written program?
• What are the basic building blocks?
• Vocabulary of words
• What rules guide how the words are put together
  to make a correct program?
• Context-Free Grammars

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Design Principles

• Type systems and Semantics
• What does a program/fragment/construct mean?
• Important for program correctness.
• Formal approaches are needed to answer this
  systematically.

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Design Principles

• Memory Management
• How do the program elements map to physical
  memory?
• Variables, data structures
• Function call, recursion
• Static and dynamic memory
• Dynamic memory management
• Objects have definite life spans
• Garbage collection
• Essential to have an understanding

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Design Principles

• Exception Handling
• How does a program prepare for unexpected events
  during its execution?
• Division by zero
• Improper/illegal input
• Exceptions
• Programs must trap exceptions and provide
  alternative paths or graceful exit.

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Famous Software Bugs

• NASA Mars Climate Orbiter destroyed due to
  incorrect orbit insertion (September 23, 1999).
• one team used English units (e.g., inches, feet
  and pounds) while the other used metric units
• Therac-25 (1985-1987)
• Six people were overexposed during radiation
  treatments for cancer by Canada's Therac-25
  radiation therapy machine
• The Ariane 5 rocket exploded on its maiden flight
  in June 1996
• Navigation package was inherited from the Ariane
  4
• The new rocket flew faster, resulting in larger
  values of some variables in the navigation
  software.  
• Shortly after launch, an attempt to convert a
  64-bit floating-point number into a 16-bit
  integer generated an overflow. 
• The error was caught, but the code that caught it
  elected to shut down the subsystem. .  
• Software Errors Cost U.S. Economy 59.5 Billion
  Annually (2002)

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Programming Paradigms

• Many different languages
• Only a few different styles of programming
• Imperative Programming
• Object-oriented Programming
• Functional Programming
• Logic Programming
• Event-Driven Programming
• Concurrent Programming

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Imperative Programming

• Program is a series of steps
• Retrieves input
• Perform some computation
• Generates output
• Essential building blocks
• Assignments
• Procedures
• Control structures
• Examples Fortran, C, Cobol

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Object-Oriented Programming

• Program is a collection of objects
• Interaction between objects is via message
  passing
• Essential building blocks
• Object modeling
• Inheritance, polymorphism
• Examples C, Java, Smalltalk

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Functional Programming

• Program is a collection of mathematical functions
• Have one or more arguments
• Return a value
• Essential building blocks
• Composition
• Recursion
• Examples Lisp, Scheme, ML

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Logic Programming

• Program is a collection of logical declarations
• Separation of logic (what) and control (how)
• Natural choice to express non-determinism
• Examples Prolog

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Event-Driven Programming

• Program is a continuous loop
• Wait for some event
• Respond to the event
• Order of event is arbitrary
• Increased attention due to GUIs
• Examples Visual Basic, Java

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Concurrent Programming

• Program is a set of cooperating processes
• Each process works on its own
• Shares information with others from time to time
• Essential building blocks
• Parallel constructs
• Examples Linda, High Performance Fortran (HPF)