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Introduction to Programming Languages

Introduction to Programming Languages. Nai-Wei Lin Department of Computer Science and Information Engineering National Chung Cheng University. Chapter 1 Introduction. Outline. What is a programming language Levels of programming languages Definition of programming languages

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Introduction to Programming Languages

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  1. Introduction to Programming Languages Nai-Wei Lin Department of Computer Science and Information Engineering National Chung Cheng University

  2. Chapter 1Introduction

  3. Outline • What is a programming language • Levels of programming languages • Definition of programming languages • Implementation of programming languages • Abstractions in programming languages • Paradigms of programming languages • Language design principles

  4. What Is a Programming Language • A natural language is designed to communicate between human • A programming language is designed to communicate between human and computers

  5. How we communicate influences how we think, and vice versa.

  6. A programming language is a notation for describing computation in computer-readable and human-readable form

  7. Computation • Computation is usually defined formally using the mathematical concept of a Turing machine • Church’s thesis states that it is not possible to build a machine that is inherently more powerful than a Turing machine

  8. Turing Completeness • A programming language is Turing complete if it can be used to describe all the computation that a Turing machine can perform • A programming language is Turing complete if it has integer variables and arithmetic operators, assignment statements, sequence statements, selection statements, and iteration statements

  9. Levels of Programming Languages • Machine languages • Assembly languages • High-level languages

  10. Definition of Programming Languages • The Syntax of a programming language specifies the structure of programs • The Semantics of a programming language specifies the meaning of programs

  11. Syntax An if-statement consists of the word “if” followed by an expression inside parentheses, followed by a statement, followed by an optional else part consisting of the word “else” and another statement.

  12. Semantics An if-statement is executed by first evaluating its expression, which must have arithmetic or pointer type, including all side effects, and if it compares unequal to 0, the statement following the expression is executed. If there is an else part, and the expression is 0, the statement following the “else” is executed.

  13. Formal Definition of Programming Languages • The Syntax of a programming language is usually formally defined by context-free grammars • The Semantics of a programming language is usually informally defined by human languages. It can be partially defined in a formal language using operational semantics, denotational semantics, or axiomatic semantics

  14. Implementation of Programming Languages • A compiler is a program that can translate programs written in a language into programs written in another language • An interpreter is a program that can understand a language and execute programs written in that language

  15. Source program Target program Input Compilers Target program Compiler Output

  16. Input Source program Output Interpreters Interpreter

  17. Virtual Machines • An interpreter can be viewed as a virtual machine that can directly execute a high level programming language • Compilers and interpreters are relativeconcepts. Many programming languages have both a compiler and an interpreter • Java has a compiler that translates the Java programs into Java byte codes. The Java virtual machine is an interpreter that can directly execute Java byte codes

  18. Abstractions in Programming Languages • A programming language provides abstractions of the computation that are easy to understand, even by persons not familiar with the underlying details of the computer

  19. Abstract 抽象 摘要 • Draw the common properties from all the instances • Adopt the essential properties from the whole system

  20. The sequence of operations to be processed The set of operations associated with each data object Abstractions Data Control Operations

  21. Abstractions • Data abstractions abstract properties of data, such as numbers, character strings, trees, which are subjects of computation • Control abstractions abstract properties of control, such as loops, conditional statements, and procedures

  22. Data Abstractions • Basic abstractions: basic data types such as integers, floating point numbers, and characters • Structured abstractions: structured data types such as arrays and records • Unit abstractions: abstract data types such as stacks, queues, trees, and graphs

  23. Control Abstractions • Basic abstractions: basic statements such as assignment statement and goto statement • Structured abstractions: structured statements such as if-statement, while-statement, and procedures • Unit abstractions: abstract data types such as stacks, queues, trees, graphs

  24. Abstraction of Operations Basic data types Basic statements Structured data types Structured statements Abstract data types

  25. High-Level Languages Abstract Operations Abstraction of Operations Machine Operations Machine Languages

  26. Paradigms of Programming Languages • Imperative programming – a series of commands: Fortran, Pascal, C, Ada • Object-oriented programming – a class of objects: Simula, Smalltalk, C++, Java • Functional programming – a collection of mathematical function definitions: Scheme, ML, Haskell • Logic programming – a collection of logical predicates: Prolog, Godel

  27. Imperative Programming int gcd(int u, int v) { int t; while (v != 0) { t = u % v; u = v; v = t; } return u; } How

  28. Object-Oriented Programming public class IntWithGcd { private int value; public IntWithGcd(int val) { value = val; } publicint intValue() { return value; } public int gcd(int v) { int z = value; int y = v; while (y != 0) { int t = u % v; z = y; y = t; } return z; } How

  29. Functional Programming u , if v = 0; gcd(u, v) = gcd (v, u % v), otherwise. gcd u v = if v == 0 then u else gcd(v (u ‘mod’ v)) What

  30. Logic Programming V = 0 gcd(U, V) = U V  0, Y = U %V, gcd(V, Y) = X  gcd(U, V) = X gcd(U, V, U) :- V = 0. gcd(U, V, X) :- not (V = 0), Y is U mod V, gcd(V, Y, X). What

  31. Language Design Criteria ? • It is very difficult to offer criteria for good programming language design • Criteria for good programming language design often conflict each other • A programming language can be a success or failure for many different reasons • Programming language design is a goal-orientd activity

  32. Efficiency • Efficiency of compiler construction: implementability • Efficiency of compiler execution: simplicity, reliability • Efficiency of program construction: writability, expressiveness • Efficiency of program execution: optimizability • Efficiency of program modification: readability, maintainability

  33. Regularity • Regularity is a measure of how well a language integrates its features, so that there are no unusual restrictions, interactions, or behaviors • Regularity can be placed in subcategories: Generality, Orthogonality, Uniformity

  34. Generality • Do constructs have as few restrictions as possible? • Functions • In Pascal, functions can be passed as parameters, but there are no function variables. • C lacks nested functions. • Scheme and ML have completely general functions • Fortran can pass variable-length array parameters, but cannot define variable-length array variables

  35. Orthogonality • Can constructs be combined in any meaningful way? • Return types of functions • In Pascal, functions can return only scalar or pointer types as values. • In C and C++, values of all types, except array types, can be returned. • In Ada and functional languages, values of all types can be returned

  36. Uniformity • Do similar things look the same, and do different things look different? • In C++, a semicolon is necessary after a class definition but forbidden after a function definition • In Pascal, returned values from functions look like assignments

  37. Other Criteria • Simplicity: make things as simple as possible, but not simpler. (Pascal, C) • Expressiveness: make it possible to express conceptual abstractions directly and simply. (Scheme, Simula67) • Extensibility: allow the programmer to extend the language in various ways. (Scheme, C++)

  38. Other Criteria • Security: programs cannot do unexpected damage. (Pascal, Java) • Preciseness: having a definition that can answer programmers and implementers questions. (Most languages today, but only one has a mathematical definition: ML) • Machine-independence: should run the same on any machine. (Java)

  39. Other Criteria • Consistent with accepted notations. (Most languages today, but not APL) • Restrictability: a programmer can program effectively in a subset of the full language. (C++: avoids runtime penalties)

  40. C++: A Case Study • Thanks to Bjarne Stroustrup, C++ is not only a great success story, but also the best-documented language development effort in history: • 1997: The C++ Programming Language, 3rd Edition (Addison-Wesley). • 1994: The Design and Evolution of C++ (Addison-Wesley). • 1993: A History of C++ 1979-1991, SIGPLAN Notices 28(3).

  41. Course Contents • Introduction • Syntax • Functional programming • Logic programming • Basic semantics • Data types • Expressions • Statements • Procedures • Modules • Exceptions • Conclusion

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