A Scheme Workshop

1. A Scheme Workshop Ben Leong NUS School of Computing 31 July 2007

2. Welcome to SoC • Help you make an informed decision on whether to choose between CS1101 and CS1101S NOT to teach you Scheme  • About which class is more suitable for YOU NOT about which is better….

3. Overview • What’s Scheme? • Why Scheme? • Module Synopsis (i.e. what to expect) • What your seniors say

4. Brief History of CS1101S • The language Scheme was designed 25 years ago at MIT to teach programming methodology • The success of the MIT programming methodology module led to its adoption in many universities worldwide • Scheme was first introduced at NUS 10 years ago • I took this class at MIT in 1994. 

5. Objectives • Teach Scheme as a programming language • Teach programming concepts • Inspire CONFIDENCE in students that ANYTHING can be solved if they try hard enough • Teach students Computational Thinking NOT! TO THINK 

6. Introduction to Scheme • Scheme is expression oriented. Type an expression and its result will be printed out. • Works with a variety of types of numbers: integers (both positive and negative), fractions (rational numbers), and real numbers

7. Introduction to Scheme • Expressions use prefix notation. • Use (+ 2 3)instead of (2 + 3) • Use (* (+ 2 3) (- 3 1))instead of (2+3)*(3-1) • There is a wealth of predefined functions • sqrtcomputes the square root of its argument. • + is also a predefined function

8. Why Scheme? • Teaching a language is futile (Here today, gone tomorrow) • Scheme is simple as a language • So we can focus on the CONCEPTS instead of clunky language rules • Let’s see for ourselves…..

9. Recursion • Express (divide) a problem into smaller similar problems • Solve the problem for a simple (base) case We are done (!) • Similar to Mathematical Induction

10. The Towers of Hanoi We have 3 pegs and a set of discs, all of different diameters. Objective: move the pile of discs to last peg, by: • moving 1 disc at a time from 1 peg to another; • never placing a disk on top of another disc with smaller diameter. Suppose you have not 3, but n discs …

11. The Towers of Hanoi • We must start somewhere…. • Suppose we have one disc …. • What if there are no discs? • Nothing to do! • Base case

12. The Towers of Hanoi We notice the following pattern: if we want to move n disks from peg a to peg c using peg b as intermediary storage, then we: • assume we know how to move n−1 disks to peg b, using peg c as intermediary storage; • we move disk n from a to c ; • we move n−1 disks from b to c, using a as intermediary storage. RECURSION

13. The Towers of Hanoi (define (move-tower size from to extra) (cond ((= size 0) #t) (else (move-tower (- size 1) from extra to) (print-move from to) (move-tower (- size 1) extra to from)))) (define (print-move from to) (newline) (display "move top disk from ") (display from) (display " to ") (display to))

14. CS1101S: Programming Methodology (Scheme) • Lectures: • Wed 10am-12pm, Fri 11am-12pm, LT15 • Recorded for webcast • Recitations: 1 hr/wk • Two or three groups: Prob Thurs, Venue TBA • Discussion Groups: 2 hr/wk • Three or four groups: TBA • Bid for group in CORS

15. Teaching Staff • Lecturer: Dr. Ben Leong, benleong@comp.nus.edu.sgOffice: S14 #06-14 Phone: 6516-4240 Hours: TBA, or by appointment • Undergraduate Discussion Group Leaders

16. Syllabus (in Brief) • Numeric computations in Scheme • Building recipes with functions • Recursion • Data structures: lists, trees • Memoization & Dynamic Programming • Generic operations • Object oriented abstractions • Java Covers core concepts of computer programming

17. Textbook : SICP • FREE!! • Available online at http://mitpress.mit.edu/sicp/full-text/book/book.html

18. Supplementary Text • ALSO FREE!! • Available online at http://gustavus.edu/+max/concrete-abstractions-pdfs/index.html

19. Scheme Interpreter • We will be using DrScheme • It’s FREE!!! • Download from: http://www.drscheme.org/

20. Assessment Overview • Tutorial participation: 10% • Problem sets: 30% • Midterm exam: 15% 3 Oct 2007 (Wed) 10am-12 pm • Practical exam: 15% 7 Nov 2007 (Wed) 10am-12 pm • Final exam: 30% 26 Nov 2007 (Mon) Morning

21. Tutorial Participation (10%) • Questions will usually be given out prior to the recitations/discussion groups, sometimes not • Assessed mainly by tutors, with some inputs from lecturer from interactions during recitations & lectures • You need to be active, participate by offering solutions, making comments and asking questions.

22. Midterm and Final Exams (15% + 30%) • Standard fare – 2 hours each • Will test concepts, NOT memory • Open-sheet • 1 x A4 sheet of notes allowed for midterm • 2 x A4 sheet of notes allowed for finals • Sample midterms available on IVLE • Sample finals available from Library

23. Problem Sets (30%) • Seven problem sets • Due approximately once every two weeks • Graded by the Undergraduate Tutors • Crucial for learning the material in this class • This is effectively the lab component of the class

24. Practical Exam (15%) “Test of the Pudding” • At the completion of Scheme syllabus • 2 hours to solve three programming problems of increasing difficulty • Sample exams available on IVLE

25. Other Highlights • Will build a Lego Mindstorm robot in the middle of the Semester • Regular Programming Contests to keep students challenged

26. CS1101S vs. CS1101 • Progression: CS1101S  CS1102S CS1101  CS1102 • Two-semester sequence • Discouraged from crossing over • CS1101S  CS1102, CS1101  CS1102S • Similarities • S and non-S versions both teach basic programming principles

27. CS1101S/02S vs. CS1101/02 • Differences • CS1101S/02S cover more advanced topics • More challenging • CS1102S covers Java + more • Good introduction to many computer science topics

28. Which to take? • Take CS1101S/02S if you want to be challenged. • If you have programmed before • No real advantage • In fact, can be a disadvantage! • If you have never programmed before • Great! You are not at a disadvantage. • Keep an open mind. • Some evidence show that female students cope better with Scheme than Java.

29. Java vs Scheme: What’s the Tradeoff? • Java: • sophisticated, mature • can be used for commercial applications • but has many underlying concepts that a beginner may find hard to understand • Scheme: • simple, elegant • easy to learn (hard to master) • designed to illustrate the concepts • will eventually learn Java anyway…. Mainly a question of personal choice (taste?)

30. What your seniors say…. I think Scheme really does bring about concepts easily. Java's messy, so messy for an amateur programmer. (on Problem Sets) They are all very difficult, but some are killers. I learnt a tiny bit of java before I attended this class and I was totally lost. Teaching introduction to programming in Scheme is a quite smart idea. I feel much better when I came back to Java at the end of this class. [What doesn’t kill you makes you strong]

31. What your seniors say…. I was warned by my seniors not to take scheme because they said it was very tough .... now when I’ve done this module , I agree that it is tough.. but it is worth the effort ..scheme makes u smarter !!! :) Do you agree that Scheme is easier than Java? 32% NO; 68% YES! Luv the class, luv the company of students, luv the interaction with teachers, bla bla bla... Scheme's cool I think we need more classmates 

32. More comments here …. • http://www.comp.nus.edu.sg/~bleong/ teaching/cs1101s06-midterm.htm • http://www.comp.nus.edu.sg/~bleong/ teaching/cs1101s06-final.htm • Just Google “cs1101s survey”!!!

33. Words of Advice • Don’t worry about the curve • Scheme is easier (or so I would claim), but doesn’t mean that CS1101S is an easier class • Take CS1101S still have to learn Java…. so it is definitely more work • Have to be prepared to work very hard in CS1101S

34. QUESTIONS

35. THANKYOU