Assignment 2 on Functional Programming

COMP 348: Principles of Programming Languages
Assignment 2 on Functional Programming
Summer 2020, sections AA and AB
May 30, 2020
Contents
1 General Information 2
2 Introduction 2
3 Ground rules 2
4 Your Assignment 2
4.1 List Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4.2 Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.3 Miscellaneous Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5 What to Submit 6
6 Grading Scheme 8
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1 General Information

Weight: 6% of the overall grade.
2 Introduction
In this assignment you will be practicing functional programming using Lisp language.
3 Ground rules
You are allowed to work on a team of 3 students at most (including yourself). Each team
should designate a leader who will submit the assignment electronically. ONLY one copy of
the assignment is to be submitted.
This is an assessment exercise. You may not seek any assistance from others while expecting
to receive credit. You must work strictly within your team). Failure to do so will
result in penalties or no credit.
4 Your Assignment
Your assignment consists of ve questions, each of which may be independently implemented.
Some require functions and some may require complete program. Refer to each question for
the details.
4.1 List Processing
For the following questions, implement the function in lisp. Some examples are provided to
illustrate the behaviour of each function. Note that Your implementation must work for all
form of possible inputs.
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Q 1. Write a lisp function that takes a list and an integer n, and returns the last n elements
of the list, as a new list, e.g.:
> (take-n '(1 2 3) 2)
(2 3)
In case n is less than 1, it returns NIL. In case n is beyond the length, the function returns
a copy of the original list.
Q 2. Write a function called reverse-cut-in-half that receives a list and creates a new list
whose elements are the rst and the second halves reversed. e.g.:
> (reverse-cut-in-half '(1 2 3))
((3) (1 2))
> (reverse-cut-in-half '((1) (2) (3) (4)))
(((3) (4)) ((1) (2)))
In case of odd length, the rst half before reversing takes the middle element.
Show the output for (reverse-cut-in-half '(a))
4.2 Structures
Q 3. Write a lisp function that receives a list as the input argument (the list is mixed up
integers, decimals, characters and nested lists) and returns a attened list containing all
the atomic elements that are numbers, without any duplication. Sample function output is
shown below:
(flatten '(1 2 (3 1) (a 2.5) (2 4.5) ((1 2))))
(1 2 3 2.5 4.5)
Note that the elements are given in the same order as they are received.
Partial marks are given if the order is not maintained.
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Q 4. Write a lisp program to check whether a binary tree is a Binary Search Tree. A Binary
Search Tree (BST) is a tree in which all the nodes follow the below-mentioned properties:
ˆ The left sub-tree of a node has a key less than or equal to its parent node's key.
ˆ The right sub-tree of a node has a key greater than to its parent node's key.
The list representing the structure of a sample binary tree is given in the following:
'(8 (3 (1 () ()) (6 (4 () ())(7 () ()))) (10 () (14 (13) ())))
Q 5. Write a function called balancedp that takes a structure and returns true if it is
balanced. A structure is balanced if number of elements and all their subelements on the
left hand side is equal to the number of elements and all their subelements on the right hand
side. e.g.:
> (balancedp '(a b c))
T
> (balancedp '(a b c d))
T
> (balancedp '(hello world (this is a test))) ; outer list
NIL ; has 3 elements
> (balancedp '(hello world (this assingment))) ; outer list
NIL ; has 3 elements
> (balancedp '((1 2) (3 (1)))
T
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4.3 Miscellaneous Programs
Q 6. Write a lisp function triangle that takes an integer as the argument and prints a triangle
of stars as shown in the following gure. If the input is 0, decimal or string, it should print
an appropriate error message. positive integers print left-justied triangles, whereas for the
negative numbers the printed triangles are right-justied.
Example:
> (triangle 2.5)
invalid number; please enter a positive or a negative integer
> (triangle 0)
invalid number; please enter a positive or a negative integer
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Q 7. The 3x + 1 Conjecture: The Collatz conjecture 1931
Let T be the transformation that sends an even integer x to x/2 and an odd integer x to
3x + 1. For all positive integers x, when we repeatedly apply the transformation T, we will
eventually reach the integer 1.
(a) Write a function collatz that takes n as its argument and returns a list with the sequence
from n to 1.
In case of invalid inputs, the function returns NIL, as well as displaying error message
to the output. Examples of invalid inputs is n not being a positive number. You are
not allowed to use any builtin functions except predicate functions to check value type.
> (collatz 4) > (collatz 3)
(2 1) (10 5 16 8 4 2 1)
> (collatz 10)
(5 16 8 4 2 1)
> (collatz 30)
(15 46 23 70 35 106 53 160 80 40 20 10 5 16 8 4 2 1)
(b) Using the above function, write a short code to print the colattz list for numbers from
1 to 20.
5 What to Submit
The assignment is to be submitted by the due date under the corresponding assignment box.
Your instructor will provide you with more details.
Submission Notes
Clearly include the names and student IDs of all members of the team in the submission.
Indicate the team leader.
IMPORTANT: You are allowed to work on a team of 3 students at most (including yourself).
Any teams of 4 or more students will result in 0 marks for all team members. If your work on
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a team, ONLY one copy of the assignment is to be submitted. You must make sure that you
upload the assignment to the correct assignment box on Moodle. No email submissions are
accepted. Assignments uploaded to the wrong system, wrong folder, or submitted via email
will be discarded and no resubmission will be allowed. Make sure you can access Moodle
prior to the submission deadline. The deadline will not be extended.
Naming convention for uploaded le: Create one zip le, containing all needed les for your
assignment using the following naming convention. The zip le should be called a#_studids,
where # is the number of the assignment, and studids is the list of student ids of all team
members, separated by (_). For example, for the rst assignment, student 12345678 would
submit a zip le named a1_12345678.zip. If you work on a team of two and your IDs are
12345678 and 34567890, you would submit a zip le named a1_12345678_34567890.zip.
Submit your assignment electronically on Moodle based on the instruction given by your
instructor as indicated above:
https://moodle.concordia.ca
Please see course outline for submission rules and format, as well as for the required demo
of the assignment. A working copy of the code and a sample output should be submitted
for the tasks that require them. A text le with answers to the dierent tasks should be
provided. Put it all in a le layout as explained below, archive it with any archiving and
compressing utility, such as WinZip, WinRAR, tar, gzip, bzip2, or others. You must keep
a record of your submission conrmation. This is your proof of submission, which you may
need should a submission problem arises.
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6 Grading Scheme
Q1 4 marks
Q2 5 marks
Q3 5 marks
Q4 5 marks
Q5 7 marks
Q6 7 marks
Q7 7 marks
Total: 40 marks.
References
1. Common-Lisp: https://common-lisp.net/downloads
2. Binary Search Tree (BST): https://en.wikipedia.org/wiki/Binary_search_tree
3. Collatz Conjecture: https://en.wikipedia.org/wiki/Collatz_conjecture
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