CSE-321 Programming Languages Overview POSTECH March 2, 2010 박성우

2 Language = Frame of Thought The language defines the frame of thought. –what you can communicate to others –what concepts you are able to think over –how you think Big question: "Does the programming language define the frame of thought in the course of programming?"

3 C Exercise: Integration Specification –input: function f from int to int range a and b –output: f(a) + f(a + 1) f(b) Solution? int integral(int (*f)(int), int a, int b) { int i, sum = 0; for (i = a; i <= b; i++) sum += f(i); return sum; } Question: what if there were no function pointer?

4 C Exercise: Derivative Specification –input: function f from float to float –output: derivative f' of f such that f'(x) = (f(x +  ) - f(x)) /  Solution?

5 Question for You What is your favorite language? –Assembly, Basic, Pascal, C, C++, C#, Java, Perl, Python, Ruby, Prolog, Lisp, SML, Haskell, Scheme,... What is its strength? What is its weakness? What is its limitation? Do you think your language defines the frame of thought?

Never (mistakenly) think that your favorite language is all you will need ever. Cf. 'Beating the Averages' by Paul Graham

Evolution of programming languages

8 Structured Programming Features –split programs into sub-sections (e.g., functional units) and reuse the sub-sections procedural programming –limited number of control structures for, while, do/while, repeat/until goto is discouraged. Pascal, Ada, C,... Enabled the development of large-scale software in 1970s –Unix operating system written in C –1st revolution in programming language history

9 Object-oriented Programming Features –focus on objects, rather than operations –hide the internal representation of an object –code reuse by inheritance or subclassing Smalltalk, C++, Java, C#,... Enabled the cooperative development of large- scale software in 1980s –2nd revolution in programming language history

10 Dominance of OO TIOBE programming community index, Feb 2010

11 Limitation of OO Programming No code reuse for different datatypes –templates in C++ –generics in Java No "first-class" functions –closures in Java No inherent support for modular programming –Classes are okay for modular programming of moderate scale. –OO does not scale afterwards. Why?

12 Functional Programming Standard ML, Haskell, Objective CAML, F#,... Savior for OO programming –templates in C++, generics in Java ) primitive forms of polymorphism in type theory –closures in Java ) functions in functional programming –modular programming ) structures and functors in functional programming F# in Microsoft Visual Studio 2010

What is the (ongoing) 3rd revolution in programming language history?

14 CPU Frequency

15 Multicore Revolution Intel reaches thermal wall, 2004 ) no more free lunch! Intel, 80-cores, 2011 source: Herb Sutter – "Software and the concurrency revolution"

16 Intel Roadmap

17 Tim Sweeney's POPL '06 Invited Talk - Last Slide

Parallel Programming: 3rd Programming Revolution ) It's no longer optional.

What is the hottest issue in programming language research? ) Verification (verifying that your software is okay)

20 Technologies for Verification Testing –white box testing, black box testing –limited assurance Model checking –verifying both software and hardware systems Static analysis –many success stories Astree, 100,000 lines of Airbus A380 control software –many industrialized tools (e.g., Sparrow of SNU) Deductive verification (theorem prover, proof assistant) –next-generation technology in verification

21 Can you trust your compiler? Critical software requires the correctness of compilers. –Compilers are far from perfect, producing unintended, erroneous code. –Unfortunately the verification of compiler is not trivial at all. Formal verification of CompCert (Xavier Leroy, 2006) –Clight to PowerPC assembly code –Verification in Coq (proof assistant)

Course Overview

23 Topics to Be Covered Basic programming language theory –inductive reasoning – -Calculus –basic type theory –modular programming (assignment) –object-orientation (lecture, assignment) –parallelism/concurrency (tentative)

24 Grading 50% assignments (heart of this course) –8 programming assignments, all in Standard ML 10% quizzes –4 quizzes (substitute for written assignments) 20% midterm 20% final Absolute grading system

25 No Cheating Read the document on the disciplinary policy –7 students cheated (out of 46 students) –2 suspicious cases We will check your programs at the end of the semester. –all your programs + those submitted in the previous years Cheating will not be tolerated. –Cheating will expel you from class and get you an F.

26 Homework by Thursday Visit the course webpage. – Visit the discussion board. –telnet pl.postech.ac.kr, board 321 Install –Standard ML –AFS client software. Read articles for fun. –A Critical Look at Programming Languages –The Free Lunch is Over: A Fundamental Turn Toward Concurrency in Software –Software and the Concurrency Revolution –Beating the Average