2. Programming Languages winter term 2010/11
Jörg Kreiker, I2+I7

3. Getting started What is your favorite PL?
Do you know any functional language?
Logic programming?
Expectations?
Implement the joke in your favorite PL

4. Popular languages: langpop.com

5. Most talked about languages

6. Meet Haskell: a straight bat
Download interpreter (hugs/ghci) and compiler (ghc) from haskell.org
Pure, lazy, functional language
Use declarative languages only
As opposed to imperative
Freely available books and tutorials
Printing 500 lines in Haskell

7. Haskell.org

8. realworldhaskell.org

9. Organization Lectures: Thursday, 12 noon – 1.30pm, 00.08.038
Mostly theory
Tutorials: Thursday, 2pm-3.30pm, tbd
First tutorial: next week
Mostly programming
Online problem solving
Discussion and comparison of languages and paradigms
Website: www2.in.tum.de/hp/Main?nid=142

10. Grading Written exam, 40 points, 90 minutes Programming project “Exen”
Implement a Haskell interpreter in Haskell
Earns you up to 4 bonus points
Due before xmas
“Exen”
Small tests during tutorials
Earn you 1 (>50%) or 2 (>75%) bonus points

11. Code of conduct Interaction, interaction, interaction
Buzz votes and polls
Ask questions (English or German)
No cell phones, no eating
1 or 2 breaks of 5-10 minutes per lecture
Laptops for online programming
Coffee is fine

13. Learning goals

14. 1
To write short error-free programs, without testing, for tasks such as binary search, and to use a formal system such as Hoare logic to verify them.

15. 2
To use language features such as higher-order functions and continuations to implement tasks such as backtracking and memoization.

16. Some modern features and techniques
Continuations
Polymorphism
First-class functions (closures, lambda)
Pattern matching
Software transactional memory
Memoization and backtracking
Exceptions
Monads

17. 3
To write concurrent programs using shared variables or message-passing, and to give rigorous informal arguments for their lack of errors.

18. 4
To specify precisely and implement correctly a simple programming language.

19. 5
To estimate the time and space requirements of basic operations on widely used data representations.

20. 6
To write a clear and error-free program of sufficient complexity – say a syntax-directed editor – that it must be structured carefully.

21. Content Haskell Prolog Laziness State I/O Continuations
Lambda calculus
Types and semantics
Prolog
Programming by search
Backtracking

22. Clarify and define formally…
Syntax vs semantics
Types
Scope and binding
Functions vs procedures
Call-by-value, call-by name, call-by need
Identifiers vs variables
State
Modularity
Polymorphism

24. The factorial functionП
fac(n) =
i=1 n i
implement the factorial function in your favorite language
discuss with your neighbor
3 minutes

25. Haskell freshman
fac n = if n == 0
then 1
else n * fac (n-1)

26. Haskell sophomore fac = \n -> if (==) n 0 then 1
else (*) n (fac ((-) n 1))

27. Haskell junior
fac 0 = 1
fac n = n * fac (n-1)

28. Haskell senior
fac n = foldr (*) [1..n]
fac n = foldl (*) [1..n]

29. Memoizing Haskell programmer
facs n = scanl (*) 1 [1..]
fac n = facs !! n

30. Continuation-passing style
facCPS k 0 = k 1
facCPS k n = facCPS (k . (n *)) (n-1)
fac = facCPS id

31. Accumulating programmer
facACC a 0 = a
facACC a n = fac (a*n) (n-1)
fac = facACC 1

32. Haskell boy scout y f = f (y f) fac = y (\f n -> if n==0 then 1
else n * f (n-1))

33. Pure madness s f g x = f x (g x) k x y = x b f g x = f (g x)
c f g x = f x g
y f = f (y f)
cond p f g x = if p x then f x else g x
fac = y (b (cond ((==) 0) (k 1))
(b (s (*)) (c b pred)))

35. Conclusion Learning goals, organization, content Haskell primer
Currying
Pattern matching
List combinators (foldr, foldl, scanl)
Iteration vs recursion
Accumulators and tail calls
Continuations
S, K, B, C, Y combinators

36. Outlook Next time: more on Haskell Lists and trees Types
More language features