The Evolution of Programming Languages

1. The Evolution of Programming Languages Day 3 Lecturer: Xiao Jia xjia@cs.sjtu.edu.cn The Evolution of PLs

2. The Object Oriented Paradigm The Evolution of PLs

3. 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 PLs

4. 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 PLs

5. 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 PLs

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

7. 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 PLs

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

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

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

11. 10 timesRepeat: [Transcript nextPutAll: ' Hi!'] message parameter of the message The Evolution of PLs

12. 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 PLs

13. CLU • 1974 • abstract data type (ADT) • CLU is designed for programming with ADTs The Evolution of PLs

14. 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 PLs

15. C++ • 1983 • superset of C • hybrid language • emphasize the stack rather than the heap • multiple inheritance • NO garbage collection The Evolution of PLs

16. Eiffel • Software Engineering was a key objective in the design of Eiffel • multiple inheritance • strong typing • assertions The Evolution of PLs

17. 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 PLs

18. 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 PLs

19. 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 PLs

20. Java • 1995 • portability • security • single inheritance • interfaces • exception handling • concurrency: threads • garbage collection The Evolution of PLs

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

22. Homework • Kevo • Beta • Blue • CLOS • Self • Io The Evolution of PLs

23. Backtracking Languages (we only talk about Prolog[1972]) The Evolution of PLs

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

25. 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 PLs

26. 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 PLs

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

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

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

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