ISBN Structure of Programming Languages Prof. Dr. Mostafa Abdel Aziem Mostafa Senior Lecturer

ISBN Module information … 1- Introduction&preliminaries 2- Describing Syntax and Semantics 3- Lexical and syntax analysis. 4- Names, binding, type checking, and Scopes 5- Data Types. 6-Expressions and Assignment Statements. 7- Statement- Level control Structures. 8- Subprograms. 9- Implementing Subprograms.

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-3 Teaching Team Prof.Dr. Mostafa Abdel Aziem mostafa Teaching assistant Mr. Mohamed Saleh Office hours: sun 10:30- 12:30 different from handout

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-4 Module Structure Lectures Tutorials Help channels Assignments & Quizzes Examination

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-5 ~12 lectures (Mon 10:30-12:00) 15 tutorials (1 hr per week) Office hours, , appointment (by ) 4 Assignments & 1 or 2 Quizzes 15% of final mark) A written examination (40% of final mark)

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-6 Concepts of Programming Languages. Sixth Edition, 2004 Robert W. Sebesta Additional Reading Principle of Programming Languages

ISBN Chapter 1 Preliminaries

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-8 Chapter 1 Topics Motivation Programming Domains Language Evaluation Criteria Influences on Language Design Language Categories Language Design Trade-Offs Implementation Methods Programming Environments

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-9 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

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-10 What makes programming languages an interesting subject? The amazing variety There are very many, very different languages A list that used to be posted occasionally on comp.lang.misc had over 2800 published languages in Often grouped into four families: { Imperative { Object-oriented { Functional { Logic

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-11 Imperative Languages Example: Factorial function in C int fact(int n) { int sofar = 1; while (n>0) sofar *= n--; return sofar; } Hallmarks of imperative languages: { Assignment { Iteration { Order of execution is critical

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-12 Functional Languages Example: Factorial function in Haskell fac 0 = 1 fac n = n * fac (n-1) Hallmarks of functional languages: { Single-valued variables { closely tied to the mathematical concept of \function" { Heavy use of recursion

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-13 Logic Languages Example: Factorial function in Prolog fact(X,1) :- X =:= 1. fact(X,Fact) :- X > 1, NewX is X - 1, fact(NewX,NF), Fact is X * NF. Hallmark of logic languages { Program expressed as rules in formal logic

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-14 Object-Oriented Languages Example: a Java denition for a kind of object that can store an integer and compute its factorial public class MyInt { private int value; public MyInt(int value) { this.value = value; }

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-15 public int getValue() { return value; } public MyInt getFact() { return new MyInt(fact(value)); } private int fact(int n) { int sofar = 1; while (n > 1) sofar *= n--; return sofar; } }

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-16 Hallmarks of object-oriented languages: { Usually imperative, plus... { Constructs to help programmers use "objects\-little bundles of data that know how to do things to themselves.

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-17 Widely Used and Not Widely Used Widely Used { Java: Quick rise to popularity since 1995 release { Java uses many ideas from C++, plus some from Mesa, Modula, and other languages { C++ uses most of C and extends it with ideas from Simula 67, Ada, Clu, ML and Algol 68

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-18 { C was derived from B, which was derived from BCPL, which was derived from CPL, which was derived from Algol 60 Not Widely Used: Algol { One of the earliest languages: Algol 58, Algol 60, Algol 68 { Never widely used { Introduced many ideas that were used in later languages, including Block structure and scope Recursive functions Parameter passing by value

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-19 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

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-20

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-21

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-22 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

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-23 Language Evaluation Criteria –Readability factors (continued) Control statements Defining data types and structures Syntax considerations –Identifier forms –Special words –Form and meaning

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-24 Language Evaluation Criteria Writability –Factors: Simplicity and orthogonality Support for abstraction Expressivity Reliability –Factors: Type checking Exception handling Aliasing Readability and writability

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-25 Language Evaluation Criteria Cost –Categories Training programmers to use language Writing programs Compiling programs Executing programs Language implementation system Reliability Maintaining programs Others: portability, generality, well-definedness

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-26 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

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-27 Von Neumann Architecture

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-28 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

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-29 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

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-30 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

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-31 Language Design Trade-Offs Reliability vs. cost of execution Readability vs. writability Flexibility vs. safety

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-32 Layered View of Computer

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-33 Levels of Language in Computing

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-34 Implementation Methods Compilation –Translate high-level program to machine code –Slow translation –Fast execution

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-35 Compilation Process

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-36 Implementation Methods Pure interpretation –No translation –Slow execution –Becoming rare

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-37 Pure Interpretation

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-38 Implementation Methods Hybrid implementation systems –Small translation cost –Medium execution speed

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-39 Hybrid Implementation System

Copyright © 2004 Pearson Addison-Wesley. All rights reserved.1-40 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++