代写CMPSC 461、代写Java，Python编程

日期：2022-03-29 10:12

CMPSC 461: Programming Language Concepts

Prof. G. Tan, Spring 2022

Programming assignment 2: Racket Programming

Total: 24 points. Due on Mar 30th at 6pm in Canvas.

1. (3 points) Write a Racket remove-when function. It takes two parameters.

The first is a boolean function f, and the second is a list l. The

remove-when function returns a list with all elements x in l such that

f(x) = #t being removed.

For example,

(remove-when (lambda (x) (> x 3)) ’(10 1 7 2))

should return the list (1 2), since both 10 and 7 are greater than 3.

Define the remove-when function by using case analysis and recursion.

2. (4 points) Write a Racket minInt function, which takes a list of numbers,

and returns its minimum element. For example, (minInt ’(7 3 6

2)) should return 2. If the input list is empty, then it should return 0.

Write the minInt function in Scheme in two steps:

(a) (2 points) Write a minInt helper function; it takes a number k

and a list of numbers, x, as arguments, and returns the number

which is the smallest among k and numbers in x. For example,

(minInt helper 5 ’(4 5 6)) should return 4.

(b) (2 points) Write the minInt function based on minInt helper.

3. (3 points) In Racket, write a higher-order function manycall that takes

three parameters: n, f, x. It calls f on x for n number of times, when

n is even, but calls f on x for n ? 1 number of times, when n is odd.

That is, manycall should return x when n = 0 or n = 1; it should

return f(f(x)) when n = 2 or n = 3; it should return f(f(f(f(x))))

when n = 4 or n = 5; etc. As an example, (manycall 7 plusOne

10) should return 16. Hint: you can use built-in predicates even?

and odd? to test whether a number is even or odd, respectively.

4. (5 points) Write a Racket function to-words that takes an integer

between 0 and 199, inclusive, as a parameter and returns a list of words

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corresponding to the integer’s reading in English. Make your function

have a small number of cases; i.e., don’t write a COND expression

with 200 cases. Example calls to your function are given below:

(to-words 13) ; should return (thirteen)

(to-words 42) ; should return (forty two)

(to-words 155) ; should return (one hundred and fifty five)

Note, in order to simplify things, we are not expecting dashes in the

output (i.e., 42 is output as “forty two” not “forty-two”). Also, if the

input number is outside of the range of [0,199], your program should

output ’error. Hint: You may want to use the built-in integer division

functions quotient and remainder.

5. (9 points) In this question, we are going to write a Racket function

wordMaxIndex that calculates the maximum index of each word that

appears in an input word list. For example, if the input is

’(time is long but life is short)

Then one output can be

((time 0) (long 2) (but 3) (life 4) (is 5) (short 6))

The index of the first word in a word list is 0; the index for the second

word is 1; etc. Therefore, in the previous example, the maximum index

for word “time” is 0; the maximum index for word “is” is 5, since “is”

appears twice, at index 1 and 5. Note that you are not asked to sort

the words in the output. Therefore, the output is correct as long as

the indexes are correct.

Do the following steps to implement the word-index program. In our

discussion, we call a word with an index a word-index pair, for example,

(short 6) and (is 5) are word-index pairs. We call a list of wordindex

pairs a word-index list.

(a) (3 points) Write a function initialWIList that takes a list of

words and creates a word-index list. The resulting word-index

list should have the right index for every word in the list. For

instance,

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(initialWIList ’(time is long but life is short))

should generate the following output:

((time 0) (is 1) (long 2) (but 3) (life 4) (is 5) (short 6))

Hint: develop initialWIList on top of a helper function initialWIListHelper,

which takes an index k and a word list l as input. It assumes that

the first word in l has index k and generates the right word-index

list. For instance,

(initialWIListHelper 4 ’(life is short))

should generate the following output:

((life 4) (is 5) (short 6))

(b) (2 points) Write a function mergeWI. It takes two inputs. The

first is a word-index pair and the second is a word-index list.

This function generates a new word-index list. If the input wordindex

pair has a corresponding pair in the word-index list with

the same word, then only the pair with the bigger index should

be kept; otherwise, the output word-index list should have the

input word-index list with the word-index pair at the end of the

list. For instance,

(mergeWI ’(is 1) ’((time 0) (is 5)))

should generate

((time 0) (is 5))

As another example

(mergeWI ’(life 4) ’((time 0) (is 5)))

should generate

((time 0) (is 5) (life 4))

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(c) (2 points) Write a function mergeByWord, which takes a wordindex

list and produces a new word-index list; the output wordindex

list should have one word-index pair for each word that

appears in the input list and the index should be the maximum

index of all indexes for that word in the input list. For instance,

if the input list is

((time 0) (is 1) (long 2) (but 3) (life 4) (is 5) (short 6))

then the output should be

((time 0) (long 2) (but 3) (life 4) (is 5) (short 6))

Write mergeByWord based on the reduce function we discussed in

class and mergeWI. The reduce function is not built-in in Racket;

you can type it in yourself:

(define (reduce f l v)

(if (null? l) v

(f (car l) (reduce f (cdr l) v))))

(d) (2 points) Finally, write a wordMaxIndex function that takes in

a list of words and outputs the right word-index list; that is, for

each word in the input, the output word-index list should contain

a pair for the word with the maximum index. Write this function

based on initialWIList and mergeByWord.

Notes For programming assignments, examples are given only for the purpose

of clarification. By no means that our tests will solely be based on those

examples. It’s your responsibility to thoroughly test your code by designing

your own test cases.

The Racket reference at https://docs.racket-lang.org/reference/

contains a list of standard procedures provided by Racket (for example, the

remainder and the square root functions). You may find them helpful during

your programming.

Submission format: Put all your code into one DrRacket file and submit

your file through Canvas. Please clearly mark your answers using comments

so that we can tell the correspondence between your code and questions.

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Please ensure that your file starts with a comment that includes your name

and your Penn State network user id.

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