Choose a problem you've previously turned in that
required one or more auxiliary functions. Re-write
this problem with the auxiliary functions hidden inside a
local block.
Review the function largest, discussed
in class on Dec. 1.
Develop a similar function
smallest which takes a non-empty list of numbers and returns the
smallest. To test whether it's reasonably efficient, test it on a list of
twenty or more numbers in decreasing order.
Develop a similar function
leftmost which takes a non-empty list of posns
and returns the one with the smallest x-coordinate.
Develop a generalized function
champion which takes a non-empty list of X's (where X is
any data type) and a function (let's call it beats?)
with the contract "X X -> boolean", and returns the element of
the list that "beats" all the others. For example,
(champion (list 5 2 4 6 3) >) "should be 6"
(champion (list 5 2 4 6 3) <) "should be 2"
Re-write smallest using champion.
Your new definition should fit on one or two reasonably short lines.
Re-write leftmost using
champion. Your new definition should fit on at most four
reasonably short lines.
Re-write the winner function from homework 8 using champion. (If you didn't
finish the winner function before, here's your second chance.)
Your new definition should fit on at most four reasonably short lines.
Note: Recall that winner returned the
name of the winner, not the whole winner. Use local
and champion to get the whole winner, and then extract the
winner's name.
To test whether your winner function is efficient enough,
test it on a long list of candidates in increasing order of votes, e.g.
(list (make-candidate 'ann 1) (make-candidate 'bob 2)
(make-candidate 'charlie 3) (make-candidate 'dolores 4)
(make-candidate 'eddie 5) (make-candidate 'frank 6) (make-candidate 'george 7)
(make-candidate 'hilda 8) (make-candidate 'ian 9) (make-candidate 'jeff 10)
(make-candidate 'karen 11) (make-candidate 'lee 12) (make-candidate 'mary 13)
(make-candidate 'ned 14) (make-candidate 'omar 15) (make-candidate 'phil 16)
(make-candidate 'quint 17) (make-candidate 'ron 18) (make-candidate 'sam 19)
(make-candidate 'tess 20) (make-candidate 'uma 21) (make-candidate 'velma 22)
(make-candidate 'wanda 23) (make-candidate 'xena 24)
(make-candidate 'yuri 25) (make-candidate 'zelda 26))
It should take less than a second. (If you wrote winner for
homework 7, test that version on the same test case and see what happens.)
Set DrScheme to the "Advanced Student" language level. You won't know how to solve this problem until Dec. 8.
Develop a function namedcount-down that
takes in a natural number and prints (using display) the
numbers from that number down to zero, each on a separate line, ending
with "blastoff!" in place of the number 0. For example, 
You won't know how to solve this problem until Dec. 8.
Develop a function named
give-raise! which takes an employee struct
(from homework 8) and
a number (e.g. 0.10 for a 10% raise), and modifies the employee
to earn that much more than before. The function returns nothing. For example,
(define joe (make-employee 'joe 50000)) (give-raise! joe 0.10) "should be nothing" joe "should be (make-employee 'joe 55000)"
Develop a function named give-raises!
which takes a list of employees and a number, and
modifies each of them with that percentage raise. Don't worry about the
return value, but look for opportunities to re-use previously-written
functions (which may require defining a local function).
For example,
(define joe (make-employee 'joe 50000)) (define mary (make-employee 'mary 60000)) (give-raises! (list joe mary) 0.10) "may return something, but I don't care" joe "should be (make-employee 'joe 55000)" mary "should be (make-employee 'mary 66000)"
Extra credit: Develop a function named
ask-and-give-raises! which takes a list of employees.
For each employee, your function will print a message on the screen with
the person's name, asking how much raise (e.g. 0.10 for a 10% raise)
that person should get;
it will then wait for the user to type a number, modify that person's
salary, and go on to the next employee. Ideally, the function should
return nothing, but don't worry about that too much.
As usual, look for opportunities
to re-use previously-written functions.
For example,
