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  1. The Evolution of Programming Languages CS 351 Mark Hennessy Dept. Computer Science NUIM CS351

  2. Ij 1. Customized Digital Computer Oj Task j Task k Ik Ok Rig different circuit for each task Mark Hennessy Dept. Computer Science NUIM CS351

  3. 2. Stored Program Computing • von Neumann showed the existence of a Universal Machine (hardware) that can be customized using control inputs to carry out different tasks. • Software is the encoding of the task to control this machine. encoding(Tj) Ij Oj Mark Hennessy Dept. Computer Science NUIM CS351

  4. Imperative Languages • Model of Computation • ALU + Memory + Input + Output (von Neumann architecture) • Levels of Abstraction (“Human Interface”) • Machine Language • Binary Representation of the task • Assembly Language • Symbolic Representation of the task Mark Hennessy Dept. Computer Science NUIM CS351

  5. Imperative Languages - FORTRAN • Stands for FORmula TRANslantion. • Invented in the 1950’s as the first high level programming language i.e used a compiler. • Hello World Example: C FORTRAN IV WAS ONE OF THE FIRST PROGRAMMING C LANGUAGES TO SUPPORT SOURCE COMMENTS WRITE (6,7) 7 FORMAT(13H HELLO, WORLD) STOP END Mark Hennessy Dept. Computer Science NUIM CS351

  6. Imperative Languages – ALGOL 60 • Stands for ALGOrithmic Language • Defined in 1960 and was the first to introduce features still in use today: block structure and syntax defined by a grammar. procedure Absmax(a) Size:(n, m) Result:(y) Subscripts:(i, k); value n, m; array a; integer n, m, i, k; real y; comment The absolute greatest element of the matrix a, of size n by m is transferred to y, and the subscripts of this element to i and k; begininteger p, q; y := 0; i := k := 1; for p:=1 step 1 until n do for q:=1 step 1 until m do if abs(a[p, q]) > y then begin y := abs(a[p, q]); i := p; k := q end end Absmax Mark Hennessy Dept. Computer Science NUIM CS351

  7. Imperative Languages - C • The most successful ALGOL type language. • Lexical variable scope and recursion • A static type system which prevents many meaningless operations • Function parameters are generally passed by value (pass-by-reference is achieved in C by explicitly passing pointer values) • Heterogeneous aggregate data types (struct in C) which allow related data elements to be combined and manipulated as a unit • A small set (around 30) of reserved keywords Mark Hennessy Dept. Computer Science NUIM CS351

  8. Functional Languages • Imperative programs are concerened with programming a series of instructions that change the state of program towards giving the solution. • Functional Programming is concerned with viewing a program as a series of mathematical functions. • Based upon the maths model of Lambda Calculus, developed by Turing, Church and Kleene in the 1930’s. • Church’s thesis says that there is no one form of computation that is any more powerful than another. • This hold true as we are studying Paradigms! Mark Hennessy Dept. Computer Science NUIM CS351

  9. Functional Languages • Turing developed a model of computation called the Turing Machine …. TCS course. • Church developed lambda calculus. • This is based on the notion of parameterised expressions, which forms the basis of Functional Programming. • Passing arguments to methods. Mark Hennessy Dept. Computer Science NUIM CS351

  10. Functional Programming • Introduced into programming the notions of: • First class and higher order functions • Polymorphism • Lists • Recursion • Constructors • Garbage Collection Mark Hennessy Dept. Computer Science NUIM CS351

  11. Functional Programming • Difference between FP and Imperative programming: IP: “To compute the gcd of a and b, check to see if a and b are equal. If so print one of them and exit. Otherwise replace the larger one by their difference and repeat.” FP: “The gcd of a and b is defined to be a when a=b, and to be the gcd of c and d when a!=b, where c is the smaller of a and b and d is their difference. To compute the gcd of a given pair of numbers, expand and simplify this definition until it finishes. Mark Hennessy Dept. Computer Science NUIM CS351

  12. Functional Languages - Lisp • Stands for List Processing • Same vintage as Fortran and ALGOL. • Allows for operations on lists • Eg car(0, 2, 4, 6) = 0 • Eg cdr(0, 2, 4, 6) = (2, 4, 6) • Lisp Program for factorials: (defun factorial (n) (if (<= n 1) 1 (* n (factorial (- n 1))))) Mark Hennessy Dept. Computer Science NUIM CS351

  13. Functional Languages - ML • Stands for Meta Language • Functional Language with syntax closer to what you are familiar with. Will be doing practicals with it! (CaML). • CaML Program for factorials. let rec fac n =    if n <= 1    then n    else n * fac(n-1);; Mark Hennessy Dept. Computer Science NUIM CS351

  14. Logic Programming • Designed to allow mathematical axioms help prove a theorem. • Based on the idea of a Horn clause • H <- B1, B2,….Bn • The arrow means “if” and the commas mean “and” • We will be studying Logic programming via Prolog Mark Hennessy Dept. Computer Science NUIM CS351

  15. Logic Programming - Prolog • Name derives from the French programmation en logique. • Dates from the early 1970’s. • Based upon Predicate Calculus, the system uses backtracking. Example Prolog Program for Factorials: factorial(0,1). factorial(N,F) :- N>0, N1 is N-1, factorial(N1,F1), F is N * F1. Mark Hennessy Dept. Computer Science NUIM CS351

  16. Object Oriented Programming • Current paradigm. We write classes such that data is hidden, ideas are abstracted and code is re-usable! In theory…. • Simula -> Smalltalk & Ada -> C++ -> Java • Sub paradigms • Aspect Oriented Programming • Generic Programming via Templates • We will use C++ to show some advanced OO features and generic programming. Mark Hennessy Dept. Computer Science NUIM CS351

  17. Scripting • Another form of programming is via scripting. • Huge amount of scripting languages, Awk, sed, Bash, Javascript, UnrealScript etc • We will intoduce scripting via Bash and Python in this course. • Python uses dynamic typing and features a very clean syntax. Multi Paradigm! Mark Hennessy Dept. Computer Science NUIM CS351

  18. Scripting - Python • Indentation is essential! • Sample factorial function: def fac ( num ): if num == 1: return 1 else : return num * fac(num-1) Mark Hennessy Dept. Computer Science NUIM CS351