preliminaries, concepts of programming languages

ISBN 0-321-19362-8
Chapter 1
Preliminaries

Copyright © 2004 Pearson Addison-Wesley. All rights reserved. 1-2
Chapter 1 Topics
• Motivation
• Programming Domains
• Language Evaluation Criteria
• Influences on Language Design
• Language Categories
• Language Design Trade-Offs
• Implementation Methods
• Programming Environments

Motivation: Why Study Programming
Languages?
• Increased ability to express ideas
• Improved background for choosing appropriate
languages
• Greater ability to learn new languages
• Understand significance of implementation
• Ability to design new languages
• Overall advancement of computing

Programming Domains
• Scientific applications
– Large number of floating point computations
• Business applications
– Produce reports, use decimal numbers and characters
• Artificial intelligence
– Symbols rather than numbers manipulated
• Systems programming
– Need efficiency because of continuous use
• Scripting languages
– Put a list of commands in a file to be executed
• Special-purpose languages

Language Evaluation Criteria
• Readability
– The most important criterium
– Factors:
• Overall simplicity
– Too many features is bad
– Multiplicity of features is bad
• Orthogonality
– Makes the language easy to learn and read
– Meaning is context independent
– A relatively small set of primitive constructs can be combined in
a relatively small number of ways
– Every possible combination is legal
– Lack of orthogonality leads to exceptions to rules

– Readability factors (continued)
• Control statements
• Defining data types and structures
• Syntax considerations
– Identifier forms
– Special words
– Form and meaning

• Writability
– Factors:
• Simplicity and orthogonality
• Support for abstraction
• Expressivity
• Reliability
– Factors:
• Type checking
• Exception handling
• Aliasing
• Readability and writability

• Cost
– Categories
• Training programmers to use language
• Writing programs
• Compiling programs
• Executing programs
• Language implementation system
• Reliability
• Maintaining programs
• Others: portability, generality, well-definedness

Influences on Language Design
• Computer architecture: Von Neumann
• We use imperative languages, at least in part,
because we use von Neumann machines
– Data and programs stored in same memory
– Memory is separate from CPU
– Instructions and data are piped from memory to
CPU
– Basis for imperative languages
• Variables model memory cells
• Assignment statements model piping
• Iteration is efficient

Von Neumann Architecture

Influences on Language Design
• Programming methodologies
– 1950s and early 1960s: Simple applications; worry
about machine efficiency
– Late 1960s: People efficiency became important;
readability, better control structures
• Structured programming
• Top-down design and step-wise refinement
– Late 1970s: Process-oriented to data-oriented
• data abstraction
– Middle 1980s: Object-oriented programming

Language Categories
• Imperative
– Central features are variables, assignment
statements, and iteration
– C, Pascal
• Functional
– Main means of making computations is by
applying functions to given parameters
– LISP, Scheme

Language Categories
• Logic
– Rule-based
– Rules are specified in no special order
– Prolog
• Object-oriented
– Encapsulate data objects with processing
– Inheritance and dynamic type binding
– Grew out of imperative languages
– C++, Java

Language Design Trade-Offs
• Reliability vs. cost of execution
• Readability vs. writability
• Flexibility vs. safety

Layered View of Computer

Implementation Methods
• Compilation
– Translate high-level program to machine code
– Slow translation
– Fast execution

Compilation
Process

• Pure interpretation
– No translation
– Slow execution
– Becoming rare

Pure Interpretation

• Hybrid implementation systems
– Small translation cost
– Medium execution speed

Hybrid
Implementation
System

Programming Environments
• The collection of tools used in software
development
• UNIX
– An older operating system and tool collection
• Borland JBuilder
– An integrated development environment for Java
• Microsoft Visual Studio.NET
– A large, complex visual environment
– Used to program in C#, Visual BASIC.NET,
Jscript, J#, or C++

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