1. CS5205Introduction1 CS5205: Foundation in Programming Languages Lecture 0 : Overview Lecturer : Chin Wei Ngan Email : chinwn@comp.nus.edu.sg Office : COM2 4-32 “Language Foundation, Extensions and Reasoning

2. CS5205Introduction2 Course Objectives Course Objectives - graduate-level course with foundation focus - languages as tools for programming - foundations for reasoning about programs - explore various language innovations

3. CS5205Introduction3 Course Outline Course Outline Lecture Topics (13 weeks) Advanced Typed Language (Haskell) http://www.haskell.org Lambda Calculus (Core Language) Interpreters Untyped Scripting Language (Python) http://www.python.org Type System for Lightweight Analysis http://www.cs.cmu.edu/~rwh/plbook/book.pdf Semantics

4. CS5205Introduction4 Administrative Matters Administrative Matters - mainly IVLE - Reading Materials (mostly online): www.haskell.org Robert Harper : Foundations of Practical Programming Languages. Free PL books : http://freeprogrammingbooks.com - Lectures + Assignments + Paper Reading+ Exam - Assignment/Project (35%) - Paper Reading (10%) - Quiz (10%) - Exam (45%)

5. CS5205Introduction5 Paper Presentation Paper Presentation Focus on Language Innovation/Application Select A Paper (Week 2) Give Presentation (Week 4/5) Possible Topics Concurrent and MultiCore Programming Software Transaction Memory GUI Programming Testing with QuickCheck IDE for Haskell SELinks (OCaml) etc A List of Papers/Conferences will be given next week.

6. CS5205Introduction6 Assignments/Project (35%) Assignments/Project (35%) Small Exercises Mini-Project List of possible projects (Week 5) Your own project A useful tool Use advanced languages, such as Haskell, Ocaml, F#, Python, Boo, etc Evaluation (i) presentation/demo (ii) draft report/paper

7. CS5205Introduction7 Why Study Foundations of PL? Why Study Foundations of PL? Language used to organize programming thoughts. Language can describe and organize computation. Language features affect how ideas are expressed. Foundation needed to support the design of good language features

8. CS5205Introduction8 Benefits of Good PL Features Benefits of Good PL Features Readability Extensible Software. Modifiability. Reusability. Correctness.

9. CS5205Introduction9 Benefits of Studying Foundations of PL Design new languages for your work/research? Inside any successful software system is a PL Emacs : Elisp Word, PPT : VBScript Quake : QuakeC Facebook : FBML, FBJS Twitter : Ruby on Rails/Scala Also: Latex, XML, SQL, PS/PDF

10. CS5205Introduction10 Benefits of Studying Foundations of PL Different language paradigm can support different approaches to a given problem. Can choose a solution that is best (or good enough) for the given problem. PL is the primary tool of choice for programmers. If properly selected, it can amplify your programming capability. Era of domain-specific programming languages.

11. CS5205Introduction11 Many Dimensions of PL Syntax – verbose vs succint. prefix vs distfix. Computational model : functional, imperative, OO or constraint-based. Memory Model : explicit deallocation, garbage collection or region-based. Typing : static vs dynamic typing; strong vs weak typing. Execution Model : compiled (C/C++), interpreted (Perl), hybrid (Java). Scoping : static vs dynamic scoping.

12. CS5205Introduction12 Advanced Language - Haskell Advanced Language - Haskell Strongly-typed with polymorphism Higher-order functions Pure Lazy Language. Algebraic data types + records Exceptions Type classes, Monads, Arrows, etc Advantages : concise, abstract, reuse Why use Haskell ? cool & greater productivity

13. CS5205Introduction13 Some Applications of FP/Haskell Some Applications of FP/Haskell Hoogle – search in code library Darcs – distributed version control Programming user interface with arrows.. How to program multicore? map/reduce and Cloud computing Bioinformatics Cryptography

14. CS5205Introduction14 Example - Haskell Program Example - Haskell Program Apply a function to every element of a list. data List a = Nil | Cons a (List a) map f Nil = Nil map f (Cons x xs) = Cons (f x) (map f xs) a type variable type is : ( a  b)  (List a)  (List b) map sqr(Cons 1 (Cons 2 (Cons 3 Nil))) ==> (Cons 1 (Cons 4 (Cons 9 Nil)))

15. CS5205Introduction15 Example - Haskell Program Example - Haskell Program Built-in List Type with syntactic sugar data [a] = [] | a:[a] map :: ( a  b)  [a]  [b] map f []= [] map f (x:xs) = (f x):(map f xs) map sqr 1:(2:(3:[])) ==> 1:(4:(9:[])) map sqr [1,2,3] ==> [1,4,9]

16. CS5205Introduction16 Paradigm : Functional Expression Problem : sum the square of a list of numbers sumsq [1,2,3,4] = 1*1 +2*2 +3*3 + 4*4. Problem : sum the square of a list of numbers sumsq [] = 0 sumsq (x:xs) = (sqr x) + (sumsq xs)

17. CS5205Introduction17 Paradigm : Imperative Loop Problem : sum the square of a list of numbers sumsq [1,2,3,4] = 1*1 +2*2 +3*3 + 4*4. In F# (Ocaml dialect) sumsq :: [Int] = Int sumsq xs = let s = ref 0 in for x in xs s := !s + x ; s

18. CS5205Introduction18 Paradigm : Function-Level Composition Sum a list: Square a list: sum [] = 0 sum (x:xs) = x + (sum xs) square xs = map sqr xs Sum a square of list: square = sum o (map sqr) square = (map sqr) | sum square xs = xs |> (map sqr) |> sum