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

2. 1. Customized Digital Computer
Task j Ij Oj
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. Mark Hennessy Dept. Computer Science NUIM CS351
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;
begin integer 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. Mark Hennessy Dept. Computer Science NUIM CS351
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. Mark Hennessy Dept. Computer Science NUIM CS351
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. Mark Hennessy Dept. Computer Science NUIM CS351
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. Mark Hennessy Dept. Computer Science NUIM CS351
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. Mark Hennessy Dept. Computer Science NUIM CS351
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