Programming Language Slides(R.W. Sebesta)

Chapter 1

Preliminaries

ISBN 0-321-33025-0

Chapter 1 Topics
• Reasons for Studying Concepts of
Programming Languages
• Programming Domains
• Language Evaluation Criteria
• Influences on Language Design
• Language Categories
• Language Design Trade-Offs
• Implementation Methods
• Programming Environments
Copyright © 2006 Addison-Wesley. All rights reserved.

1-2

Reasons for Studying Concepts of
Programming Languages
• Increased ability to express ideas
• Improved background for choosing appropriate languages
• Increased ability to learn new languages
• Better understanding of significance of implementation • Overall advancement of computing

Copyright © 2006 Addison-Wesley. All rights reserved.

1-3

Programming Domains
• Scientific applications
– Large number of floating point computations
– Fortran

• Business applications
– Produce reports, use decimal numbers and characters
– COBOL

• Artificial intelligence
– Symbols rather than numbers manipulated
– LISP

• Systems programming
– Need efficiency because of continuous use
– C

• Web Software
– Eclectic collection of languages: markup (e.g., XHTML), scripting (e.g., PHP), general-purpose (e.g., Java)

Copyright © 2006 Addison-Wesley. All rights reserved.

1-4

Language Evaluation Criteria
• Readability the ease with which
Readability:
programs can be read and understood
• Writability the ease with which a
Writability:
language can be used to create programs
• Reliability conformance to specifications
Reliability:
(i.e., performs to its specifications)
• Cost the ultimate total cost
Cost:

Copyright © 2006 Addison-Wesley. All rights reserved.

1-5

Evaluation Criteria: Readability
• Overall simplicity
–
–
–

A manageable set of features and constructs
Few feature multiplicity (means of doing the same operation)
Minimal operator overloading

• Orthogonality
–

A relatively small set of primitive constructs can be combined in a relatively small number of ways
– Every possible combination is legal

• Control statements
–

The presence of well-known control structures (e.g., while statement) • Data types and structures
–

The presence of adequate facilities for defining data structures

• Syntax considerations
– Identifier forms: flexible composition
– Special words and methods of forming compound statements
– Form and meaning: self-descriptive constructs, meaningful keywords Copyright © 2006 Addison-Wesley. All rights reserved.

1-6

Evaluation Criteria: Writability
• Simplicity and orthogonality
– Few constructs, a small number of primitives, a small set of rules for combining them

• Support for abstraction
– The ability to define and use complex structures or operations in ways that allow details to be ignored

• Expressivity
– A set of relatively convenient ways of specifying operations
– Example: the inclusion of for statement in many modern languages
Copyright © 2006 Addison-Wesley. All rights reserved.

1-7

Evaluation Criteria: Reliability
• Type checking
– Testing for type errors

• Exception handling
– Intercept run-time errors and take corrective measures

• Aliasing
– Presence of two or more distinct referencing methods for the same memory location

• Readability and writability
– A language that does not support “natural” ways of expressing an algorithm will necessarily use “unnatural” approaches, and hence reduced reliability

Copyright © 2006 Addison-Wesley. All rights reserved.

1-8

Evaluation Criteria: Cost
• Training programmers to use language
• Writing programs (closeness to particular applications) • Compiling programs
• Executing programs
• Language implementation system: availability of free compilers
• Reliability: poor reliability leads to high costs • Maintaining programs
Copyright © 2006 Addison-Wesley. All rights reserved.

1-9

Evaluation Criteria: Others
• Portability
– The ease with which programs can be moved from one implementation to another

• Generality
– The applicability to a wide range of applications

• Well-definedness
– The completeness and precision of the language’s official definition

Copyright © 2006 Addison-Wesley. All rights reserved.

1-10

Influences on Language Design
• Computer Architecture
– Languages are developed around the prevalent computer architecture, known as the von
Neumann architecture

• Programming Methodologies
– New software development methodologies (e.g., object-oriented software development) led to new programming paradigms and by extension, new programming languages

Copyright © 2006 Addison-Wesley. All rights reserved.

1-11

Computer Architecture Influence
• Well-known computer architecture: Von Neumann
• Imperative languages, most dominant, because of von Neumann computers
–
–
–
–

Data and programs stored in 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 (because instructions are stored in adjacent cells of memory)

Copyright © 2006 Addison-Wesley. All rights reserved.

1-12

The von Neumann Architecture

Copyright © 2006 Addison-Wesley. All rights reserved.

1-13

Programming Methodologies Influences
• 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
– Data abstraction + inheritance + polymorphism

Copyright © 2006 Addison-Wesley. All rights reserved.

1-14

Language Categories
• Imperative
– Central features are variables, assignment statements, and iteration – Examples: C, Pascal

• Functional
– Main means of making computations is by applying functions to given parameters
– Examples: LISP, Scheme

• Logic
– Rule-based (rules are specified in no particular order)
– Example: Prolog

• Object-oriented
– Data abstraction, inheritance, late binding
– Examples: Java, C++

• Markup
– New; not a programming language, but used to specify the layout of information in Web documents
– Examples: XHTML, XML
Copyright © 2006 Addison-Wesley. All rights reserved.

1-15

Language Design Trade-Offs
• Reliability vs. cost of execution
– Conflicting criteria
– Example: Java demands all references to array elements be checked for proper indexing but that increases execution costs

• Readability vs. writability
– Another conflicting criteria
– Example: APL provides many powerful operators (and a large number of new symbols), allowing complex computations to be written in a compact program but at the cost of poor readability

• Writability (flexibility) vs. reliability
– Another conflicting criteria
– Example: C++ pointers are powerful and very flexible but not reliably used
Copyright © 2006 Addison-Wesley. All rights reserved.

1-16

Implementation Methods
• Compilation
– Programs are translated into machine language • Pure Interpretation
– Programs are interpreted by another program known as an interpreter

• Hybrid Implementation Systems
– A compromise between compilers and pure interpreters
Copyright © 2006 Addison-Wesley. All rights reserved.

1-17

Layered View of Computer
The operating system and language implementation are layered over
Machine interface of a computer Copyright © 2006 Addison-Wesley. All rights reserved.

1-18

Compilation
• Translate high-level program (source language) into machine code (machine language)
• Slow translation, fast execution
• Compilation process has several phases:
– lexical analysis: converts characters in the source program into lexical units
– syntax analysis: transforms lexical units into parse trees which represent the syntactic structure of program
– Semantics analysis: generate intermediate code
– code generation: machine code is generated

Copyright © 2006 Addison-Wesley. All rights reserved.

1-19

The Compilation Process

Copyright © 2006 Addison-Wesley. All rights reserved.

1-20

Additional Compilation Terminologies
• Load module (executable image): the user and system code together
• Linking and loading the process of loading: collecting system program and linking them to user program

Copyright © 2006 Addison-Wesley. All rights reserved.

1-21

Execution of Machine Code
• Fetch-execute-cycle (on a von Neumann architecture) initialize the program counter repeat forever fetch the instruction pointed by the counter increment the counter decode the instruction execute the instruction end repeat

Copyright © 2006 Addison-Wesley. All rights reserved.

1-22

Von Neumann Bottleneck
• Connection speed between a computer’s memory and its processor determines the speed of a computer
• Program instructions often can be executed a lot faster than the above connection speed; the connection speed thus results in a bottleneck
• Known as von Neumann bottleneck; it is the primary limiting factor in the speed of computers Copyright © 2006 Addison-Wesley. All rights reserved.

1-23

Pure Interpretation
• No translation
• Programs are interpreted by another program called an interpreter.
• Easier implementation of programs (run-time errors can easily and immediately displayed)
• Slower execution (10 to 100 times slower than compiled programs)
• Often requires more space
• Becoming rare on high-level languages
• Significant comeback with some Web scripting languages (e.g., JavaScript)
Copyright © 2006 Addison-Wesley. All rights reserved.

1-24

Pure Interpretation Process

Copyright © 2006 Addison-Wesley. All rights reserved.

1-25

Hybrid Implementation Systems
• A compromise between compilers and pure interpreters • A high-level language program is translated to an intermediate language that allows easy interpretation
• Faster than pure interpretation
• Examples
– Perl programs are partially compiled to detect errors before interpretation
– Initial implementations of Java were hybrid; the intermediate form, byte code, provides portability to any machine that has a byte code interpreter and a run-time system (together, these are called Java Virtual Machine)
Copyright © 2006 Addison-Wesley. All rights reserved.

1-26

Hybrid Implementation Process

Copyright © 2006 Addison-Wesley. All rights reserved.

1-27

Just-in-Time Implementation Systems
• Initially translate programs to an intermediate language
• During execution, it compiles intermediate code into machine code when they are called
• Machine code version is kept for subsequent calls • JIT systems are widely used for Java programs • .NET languages are implemented with a JIT system Copyright © 2006 Addison-Wesley. All rights reserved.

1-28

Preprocessors
• Preprocessor macros (instructions) are commonly used to specify that code from another file is to be included
• A preprocessor processes a program immediately before the program is compiled to expand embedded preprocessor macros
• A well-known example: C preprocessor
– expands #include, #define, and similar macros Copyright © 2006 Addison-Wesley. All rights reserved.

1-29

Programming Environments
• The collection of tools used in software development • UNIX
– An older operating system and tool collection
– Nowadays often used through a GUI (e.g., CDE, KDE, or
GNOME) that run on top of UNIX

• 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++
Copyright © 2006 Addison-Wesley. All rights reserved.

1-30

Summary
• The study of programming languages is valuable for a number of reasons:
– Increase our capacity to use different constructs
– Enable us to choose languages more intelligently
– Makes learning new languages easier

• Most important criteria for evaluating programming languages include:
– Readability, writability, reliability, cost

• Major influences on language design have been machine architecture and software development methodologies • The major methods of implementing programming languages are: compilation, pure interpretation, and hybrid implementation
Copyright © 2006 Addison-Wesley. All rights reserved.

1-31