1. Copyright © 1998 by Addison Wesley Longman, Inc. 1 Concepts of Programming Languages Chapter 1

2. Copyright © 1998 by Addison Wesley Longman, Inc. 2 Why study concepts of PLs? To increase capacity to express programming concepts To improve background for choosing appropriate languages To increase ability to learn new languages To better understand the significance of implementation To increase ability to design new languages Overall advancement of computing

3. Copyright © 1998 by Addison Wesley Longman, Inc. 3 Programming Domains Scientific applications Business applications Artificial intelligence Systems programming Scripting languages Special purpose languages Others?

4. Copyright © 1998 by Addison Wesley Longman, Inc. 4 Language Evaluation Criteria Readability –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 –Control statements –Data type and structures –Syntax considerations

5. Copyright © 1998 by Addison Wesley Longman, Inc. 5 Evaluation Criteria (continued) Writability –Simplicity and orthogonality –Support for abstraction –Expressivity Reliability –Type checking –Exception handling –Aliasing –Readability and writability

6. Copyright © 1998 by Addison Wesley Longman, Inc. 6 Evaluation criteria (continued) Cost –Programmer training –Software creation –Compilation –Execution –Compiler cost –Poor reliability –Maintenance Others –Portability –Generality –Well-definedness

7. Copyright © 1998 by Addison Wesley Longman, Inc. 7 Primary influences on language design Computer architecture –We use imperative languages, at least in part, because we use von Neumann machines Programming methodologies –1950s and early 1960s: Simple applications; worry about machine efficiency –Late 1960s: People efficiency became important; readability, better control structures –Late 1970s: Data abstraction –Middle 1980s: Object-oriented programming

8. Copyright © 1998 by Addison Wesley Longman, Inc. 8 Language Categories Imperative (or Procedural) Functional Logic Object-oriented (closely related to Imperative)

9. Copyright © 1998 by Addison Wesley Longman, Inc. 9 Language Design Trade-offs Reliability versus cost of execution Writability versus readability Flexibility versus safety

10. Copyright © 1998 by Addison Wesley Longman, Inc. 10 Implementation Methods Compilation –Translate high-level program to machine code –Slow translation –Fast execution Pure interpretation –No translation –Slow execution – Becoming rare Hybrid implementation systems –Small translation cost –Medium execution speed

11. Copyright © 1998 by Addison Wesley Longman, Inc. 11 Programming Environments The collection of tools used in software development UNIX –An old operating system and tool collection Microsoft Visual C++ –A large, complex visual environment Smalltalk –A language processor/environment