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

• Whats 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 (23)(3-1)
• There is a wealth of predefined functions
• sqrt computes 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
• Lets 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))

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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_at_comp.nus.edu.s
  gOffice S14 06-14
• Phone [phone]
• 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

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Textbook SICP

• FREE!!
• Available online at http//mitpress.mit.edu/sicp/f
  ull-text/book/book.html

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Supplementary Text

• ALSO FREE!!
• Available online at http//gustavus.edu/max/concr
  ete-abstractions-pdfs/index.html

19
Scheme Interpreter

• We will be using DrScheme
• Its 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

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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 Whats 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 doesnt kill you makes you strong

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What your seniors say.

• I was warned by my seniors not to take scheme
  because they said it was very tough .... now when
  Ive 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

• Dont worry about the curve
• Scheme is easier (or so I would claim), but
  doesnt 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