Feb 28
March 7
March 14
More complicated recursions
Tree recursion, etc.
Number-spelling Miniproject (#2)
Higher order procedures
March 21
Spring Break
March 28
Tic-Tac-Toe – read SS chapter 10!
Case Study: Making Change (tree-recursion)
April 4
Elections mini-project (#3)
April 11
Midterm #2 (during lecture)
Extending sentences, words to lists (in lab)
Advanced list processing (recursion)
Start on the big project
April 18
April 25
and on…
Work on the big project (check-off 1, 2)
Programming Style and Grading
• During grading, we are going to start
becoming “more strict” on style issues
– Starting with miniproject #3
– 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?
• Avoid nesting conditional statements
• Keep procedures small !
• Good names for procedures and
parameters
• Adequate comments
– Above and within procedures
• Put tests cases in a comment block
• Indent to aid program comprehension
Midterm 2
• Midterm 2: April 11th (next Monday).
– In the lecture slot (5-6 pm, 105 North Gate)
– Practice exam in reader (do this all at once)
– Check announcements for more practice
items and solutions.
• Review session this Sunday, April 10th,
10-12. 430 Soda (Wozniak lounge).
– Email problem requests to Fu, Elham, and
Nate.
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
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)
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
Repeated (this is hard)
> (repeated butfirst 3)
 #[closure arglist=(x) d81d70]
> ((repeated butfirst 3) '(a b c d e f g))
 (d e f g)
> ((repeated butlast 3) '(a b c d e f g))
 (a b c d)
• What does the function that (repeated butfirst 3)
returns look like?
• Write repeated
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
(#f
#t
#t
#f
#f
23) ((new york) 45) )
…)
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!