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# COMP3411/9414/9814 Assignment 1 Prolog Programming solved

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## Specification

In this assignment, you are to write Prolog procedures to perform some list and tree operations. The aim of the
assignment is to give you experience with typical Prolog programming techniques.

At the start of your program, place a comment containing your full name, student number and assignment
name. You may add additional information like the date the program was completed, etc. if you wish.
At the start of each Prolog predicate that you write, write a comment describing the overall function of the
predicate.
Advice on the use of comments and meaningful identifiers in Prolog can be found under comments in the
Prolog Dictionary.

A significant part of completing this assignment will be testing the code you write to make sure that it works
correctly. To do this, you will need to design test cases that exercise every part of the code.
You should pay particular attention to “boundary cases”, that is, what happens when the data you are testing
with is very small, or in some way special. For example:

• What happens when the list you input has no members, or only one member?
• Does you code work for lists with both even and odd numbers of members?
• Does your code work for negative numbers?

Note: not all of these matter in all cases, so for example with sqrt_table, negative numbers don’t have square
roots, so it doesn’t make sense to ask whether your code works with negative numbers.
With each question, some example test data are provided to clarify what the code is intended to do. You need to
design further test data. Testing, and designing test cases, is part of the total programming task.

It is important to use exactly the names given below for your predicates, otherwise the automated testing
procedure will not be able to find your predicates and you will lose marks. Even the capitalisation of your
predicate names must be as given below.
1. Write a predicate sumsq_neg(Numbers, Sum) that sums the squares of only the negative numbers in a list
of numbers. Example:
?­ sumsq_neg([1,­3,­5,2,6,8,­2], Sum).
Sum = 38;
false

This example computes (­3)*(­3) + (­5)*(­5) + (­2)*(­2). Think carefully about how the predicate
should behave on the empty list — should it fail or is there a reasonable value that Sum can be bound to?
2. For the purposes of the examples in this question, assume that the following facts have been loaded into
Prolog:
likes(mary, apple).
likes(mary, pear).
likes(mary, grapes).
likes(tim, mango).

likes(tim, apple).
likes(jane, apple).
likes(jane, mango).
NOTE: do not include these in your solution file.

Write a predicate all_like_all(Who_List, What_List) that takes a list of people Who_List and a list of
items What_List and succeeds if every person in Who_List likes every item in What_List, according to the
predicate likes(Who, What). Your predicate should also succeed if either Who_List or What_List is empty.
Examples:
?­ all_like_all([jane,tim],[apple,mango]).
true ;
false.
?­ all_like_all([mary,tim],[apple,grapes]).
false.
?­ all_like_all([],[bananas]).
true ;
false.

Note that your all_like_all predicate will be tested with different likes(Who, What) facts to those in the
examples.
3. Write a predicate sqrt_table(N, M, Result) that binds Result to the list of pairs consisting of a number
and its square root, from N down to M, where N and M are non-negative integers, and N >= M. For example:
sqrt_table(7, 4, Result).
Result = [[7, 2.6457513110645907], [6, 2.449489742783178], [5, 2.23606797749979], [4, 2.0]] ;
false.

?­ sqrt_table(7, 8, Result).
false.
Note that the Prolog built-in function sqrt computes square roots, and needs to be evaluated using is to
actually compute the square root:
?­ X is sqrt(2).
X = 1.4142135623730951.
?­ X = sqrt(2).
X = sqrt(2).

4. Write a predicate chop_up(List, NewList) that takes List and binds NewList to List with all sequences
of successive increasing whole numbers replaced by a two-item list containing only the first and last
number in the sequence. An example of successive increasing whole numbers is: 19,20,21,22. (Note that
the numbers have to be successive in the sense of increasing by exactly 1 at each step.) For example:
?­ chop_up([9,10,5,6,7,3,1], Result).
Result = [[9, 10], [5, 7], 3, 1] ;
false.

?­ chop_up([1,3,2,3,4], Result).
Result = [1, 3, [2, 4]] ;
false.
In this example, the sequence 9,10 has been replaced by [9,10], the sequence 5,6,7 has been replaced by
[5, 7], and 2,3,4 has been replaced by [2, 4].

5. For this question we consider binary expression-trees whose leaves are either of the form tree(empty,
Num, empty) where Num is a number, or tree(empty, z, empty) in which case we will think of the letter z
as a kind of “variable”. Every tree is either a leaf or of the form tree(L, Op, R) where L and R are the left
and right subtrees, and Op is one of the arithmetic operators ‘+’, ‘­’, ‘*’, ‘/’ (signifying addition,
subtraction, multiplication and division).

Write a predicate tree_eval(Value, Tree, Eval) that binds Eval to the result of evaluating the
expression-tree Tree, with the variable z set equal to the specified Value. For example:
?­ tree_eval(2, tree(tree(empty,z,empty),
‘+’,tree(tree(empty,1,empty),
‘/’,tree(empty,z,empty))), Eval).
Eval = 2.5 ;
false.
?­ tree_eval(5, tree(tree(empty,z,empty),
‘+’,tree(tree(empty,1,empty),
‘/’,tree(empty,z,empty))), Eval).
Eval = 5.2 ;
false.Illustration of the tree used in the example above.

## Testing

This assignment will be marked on functionality in the first instance. However, you should always adhere to
good programming practices in regard to structure, style and comments, as described in the Prolog Dictionary.
Submissions which score very low in the automarking will be examined by a human marker, and may be
awarded a few marks, provided the code is readable.

Your code must work under the version of SWI Prolog used on the Linux machines in the UNSW School of
Computer Science and Engineering. If you develop your code on any other platform, it is your responsibility to
re-test and, if necessary, correct your code when you transfer it to a CSE Linux machine prior to submission.
Your code will be run on a few simple tests when you submit.

So, it is a good idea to submit early and often so
that potential problems with your code can be detected early. You will be notified at submission time if your
code produces any compiler warnings. Please ensure that your final submission does not produce any such
warnings (otherwise, marks will be deducted).

Put the Prolog code for all problems into a single file for submission purposes.
COMP3411 students: to hand in, log in to a School of CSE Linux workstation or server, make sure that your
program is in the current working directory, and use the Unix command:
% give cs3411 prolog mycode.pl

where mycode.pl is replaced by the name of the file with your code in it.
COMP9414/9814 students: to hand in, log in to a School of CSE Linux workstation or server, make sure that
your program is in the current working directory, and use the Unix command:
% give cs9414 prolog mycode.pl

where mycode.pl is replaced by the name of the file with your code in it.
Please make sure your code works on CSE’s Linux machines and generates no warnings. Remove all test
code from your submission, including that for question 2. Make sure you have named your predicates
correctly.

You can submit as many times as you like – later submissions will overwrite earlier ones. You can check that