CS3 Fall 2005

Lecture 11:

Finish higher order functions

Midterm Prep

Oct 31 More HOF – "tic-tac-toe" program: SS chapter 10!– "Change Making" case study, in the reader

Nov 7 Miniproject #3: Election-processing– Thursday a catch-up day, Friday is a holiday– MiniProject #3 due Thur/Fri: plan ahead!

Nov 14 Midterm #2

Lab: Lists (extending words and sentences)

Nov 21 Start on the project: check-off #1

Nov 28 Work on the project: checks #2

Dec 5 Checkoff #3, finish the project

Dec 17 Final Exam (midterm #3)

Programming Style and Grading

• During grading, we are going to start becoming “more strict” on style issues– MiniProject #3 will be the start– For the big project, style is important

• Why?– Program maintenance: 6 months later, will

you know what your code does?– Code “literacy”: sharing code

What issues of style matter?

• Keep procedures small !

• Good names for procedures and parameters

• Adequate comments– Above and within procedures

• Avoid nesting conditional statements

• Put tests cases in a comment block

• Indent to aid program comprehension

Midterm 2

• Midterm 2: Nov. 14th (next Monday). – In the lecture slot plus 30 minutes

(4-5:30 pm, 120 Latimer)– Practice exam in reader (do this all at once)– Check announcements for more practice

items and solutions.

• Review session – this Wednesday (Nov. 9), 7-9 p.m.– 306 Soda Hall (HP Auditorium).

What does midterm #2 cover?– Advanced recursion (accumulating, multiple

arguments, etc.)– All of higher order functions– Those "big" homeworks (bowling, compress, and

occurs-in)– Elections miniproject– Reading and programs:

• Change making, • Difference between dates #3 (HOF), • tic-tac-toe

– SS chapters 14, 15, 7, 8, 9, 10– Everything before the first Midterm (although, this

won't be the focus of a question)

When do you NEED lambda?

1. When you need the context

(add-suffix '-is-great '(nate sam mary)) (nate-is-great sam-is-great mary-is-great)

2. When you need to make a function on the fly

Procedures that make procedures

• Generally, name procedures that create procedures "make-XXX"

(make-bookends 'o) #[closure arglist=(inner-wd) d7d0e0]

((make-bookends 'o) 'hi) ohio

((make-bookends 'to) 'ron) toronto

(define tom-bookend (make-bookends 'tom))

(tom-bookends "") tomtom

Write successive-concatenation

(sc '(a b c d e)) (a ab abc abcd abcde)

(sc '(the big red barn)) (the thebig thebigred thebigredbarn)

(define (sc sent) (accumulate (lambda ?? ) sent))

make-decreasing

• make-decreasing – Takes a sentence of numbers– Returns a sentence of numbers, having

removed elements of the input that were not larger than all numbers to the right of them.

(make-decreasing '(9 6 7 4 6 2 3 1))

(9 7 6 3 1)

(make-decreasing '(3)) (3)

Chips and Drinks

(snack 1 2) 3

– This includes (chip, drink, drink), (drink, chip, drink), and (drink, drink, chip).

(snack 2 2) 6

– (c c d d), (c d c d), (c d d c)(d c c d), (d c d c), (d d c c)

"I have some bags of chips and some drinks. How many different ways can I finish all of

these snacks if I eat one at a time?

Lists (after the midterm)

• Lists are containers, like sentences where each element can be anything– Including, another list

((beatles 4) (beck 1) ((everly brothers) 2) … )

((california 55) (florida 23) ((new york) 45) )

(#f #t #t #f #f …)

List constructors

• cons– Takes an element and a list– Returns a list with the element at the front, and the list

contents trailing

• Append– Takes two lists– Returns a list with the element of each lists put

together

• List– Takes any number of elements– Returns the list with those elements

List selectors

• car– Like first

• cdr – Like butfirst

Common list procedures

• Map = every• Filter = keep• Reduce = accumulate

• Null? = empty?

• Recursion is just the same!