The Evolution of Programming Languages Day 3 Lecturer: Xiao Jia The Evolution of PLs1

The Object Oriented Paradigm The Evolution of PLs2

Hoare 1968 A fundamental feature of our understanding of the world is that we organize our experience as a number of distinct object We often need to construct within the computer a model of that aspect of real or conceptual world The Evolution of PLs3

Simula Simula I and Simula 67 Purpose: to model systems A system is a collection of interacting processes A process can be represented during program execution by multiple procedures each with its own Algol-style stacks The Evolution of PLs4

A Simula Class class Account (real balance); begin procedure Deposit (real amount) balance := balance + amount; procedure Withdraw (real amount) balance := balance - amount; end; The Evolution of PLs5

Use A Simula Class ref (Account) myAccount; MyAccount := new Account(1000); // inherit from Account Account class ChequeAccount (real amount); The Evolution of PLs6

Features coroutines: simulation of concurrent processes multiple stacks: to support coroutines classes: combine data & collection of functions prefixing: now as known as inheritance garbage collection The Evolution of PLs7

Smalltalk 1969 (development) – 1972 (appear) first implemented using BASIC inspired by Simula and LISP The Evolution of PLs8

Six Principles 1.Everything is an object 2.Objects communicate by sending and receiving messages (in terms of objects) 3.Objects have their own memory 4.Every object is an instance of a class (which must be an object) 5.The class holds the shared behavior for its instances 6.To evaluate a program list, control is passed to the first object and the remainder is treated as its message The Evolution of PLs9

10 timesRepeat: [Transcript nextPutAll: ' Hi!'] The Evolution of PLs10 receiver

10 timesRepeat: [Transcript nextPutAll: ' Hi!'] The Evolution of PLs11 message parameter of the message

First practical Smalltalk developed in 1976 at Xerox Research Center an object has private data and public functions inheritance tree with Object as its root all classes inherit directly or indirectly from the class Object blocks coroutines garbage collection The Evolution of PLs12

CLU 1974 abstract data type (ADT) CLU is designed for programming with ADTs The Evolution of PLs13

Implement a set of integers intset = cluster is create, insert, delete, member, size, choose rep = array[int] create = proc () returns (cvt) return (rep$new()) end create insert = proc (s: intset, x: int) if ~member(s, x) then rep$addh(down(s), x) end end insert member = proc (s: cvt, x: int) returns (bool) return (getind(s, x) <= rep$high(s)) end member.... end intset The Evolution of PLs14

C superset of C hybrid language emphasize the stack rather than the heap multiple inheritance NO garbage collection The Evolution of PLs15

Eiffel Software Engineering was a key objective in the design of Eiffel multiple inheritance strong typing assertions The Evolution of PLs16

Eiffel does not have … global variables enumerations subranges goto, break, continue procedure variables casts pointer arithmetic I/O defined by libraries rather than built into the language The Evolution of PLs17

Programming by Contract defensive programming sqrt (x: real): real is require x >= 0.0 Result := square root of x ensure abs(Result * Result / x - 1.0) <= 1e-6 end The Evolution of PLs18

Repeated Inheritance class House feature address: String value: Money end class Residence inherit House rename value as residenceValue end class Business inherit House rename value as businessValue end class HomeBusiness inherit Residence Business.... end The Evolution of PLs19

Java 1995 portability security single inheritance interfaces exception handling concurrency: threads garbage collection The Evolution of PLs20

Exercise Byte codes provide portability. Can you suggest any other advantages of using byte codes? The Evolution of PLs21

Homework Kevo Beta Blue CLOS Self Io The Evolution of PLs22

Backtracking Languages (we only talk about Prolog[1972]) The Evolution of PLs23

A Family parent(pam, bob). parent(tom, bob). parent(tom, liz). parent(bob, ann). parent(bob, pat). parent(pat, jim). The Evolution of PLs24 Facts

Prolog Queries ?- parent(tom, liz). yes ?- parent(tom, jim). no ?- parent(pam, X). X = bob ?- parent(bob, C). C = ann C = pat ?- parent(P, jim), parent(G, P). P = pat G = bob The Evolution of PLs25

Adding Rules grandparent(G, C) :- parent(G, P), parent(P, C). sibling(X, Y) :- parent(P, X), parent(P, Y), different(X, Y). ?- sibling(pat, X). X = ann The Evolution of PLs26

Recursive Rules ancestor(A, X) :- parent(A, X). ancestor(A, X) :- ancestor(A, P), parent(P, X). ?- ancestor(pam, jim). yes The Evolution of PLs27

Cut minimum(X, Y, X) :- X <= Y. minimum(X, Y, Y) :- X > Y. The Evolution of PLs28

Cut minimum(X, Y, X) :- X <= Y, !. minimum(X, Y, Y) :- X > Y, !. The Evolution of PLs29

Cut different(X, X) :- !, fail. different(X, Y). ?- different(Tom, Tom). no ?- different(Ann, Tom). yes The Evolution of PLs30