Description
The goal of this assignment is to try out logic-programming in Prolog.
The assignment is broken into three parts. Part 1 focuses on writing some basic queries and rules.
Part 2 is to implement HW-7 (basic OCaml functions) using Prolog. Part 3 is to implement some
basic recursive list processing functions (from HW-8) in Prolog. Each part will be implemented in
a diferent file (hw10a.pl, hw10b.pl, and hw11c.pl).
Part 1: Queries. Use the movies.pl prolog file provided in the starter code for this assignment.
The file represents a database (i.e., set of facts) containing information on movies, actors/actresses,
and directors:
• movies(M,Y) states that a movie M was released in year Y.
• director(M,D) states that a movie M was directed by a director D.
• actor(M,A,R) states that actor A played the role R in the movie M.
• actress(M,A,R) states that actress A played the role R in the movie M.
Step 1. Using the swipl interpreter, load the movies.pl file and write the following queries.
As an example, the following query finds the names of movies in the movies.pl database:
?- consult(`movies.pl’).
% movies.pl compiled 0.03 sec, 2,597 clauses
true.
?- movie(M,_).
M = barton_fink ;
M = the_big_lebowski ;
M = blade_runner ;
… etc …
1. Write a query to find movies that were released in 2006.
2. Write a query to find movies that were released in the 1980’s (Hint: Y < 1990 restricts Y
values to be less than 1990.)
3. Write a query to find directors of movies released in 1998.
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4. Write a query to find actors in a movie that they also directed.
5. Write a query to find movies in which Frances McDormand and Holly Hunter were co-stars.
Step 2. In the file hw10a.pl, implement the following rules. You should import (consult)
movies.pl in hw10a.pl as follows:
:- consult(`movies.pl’).
And then within the interpreter, you can load your file (which will also load movies.pl) as follows:
?- consult(`hw10a.pl’).
6. Write rules for a relation star(M,A) such that A is either an actor or actress in movie M. (Note:
Do not use the `;’ operator.)
7. Write a rule for a relation co_star(A1,A2) such that A1 and A2 were two different stars in the
same move. (Hint: to ensure two values are not equivalent use the \== comparison operator.)
8. Write a rule for a relation starred_2(A,Y) to find actresses and actors that starred in 2
different movies in the same year.
For questions 1–5, write your queries as comments in hw10a.pl. Be sure to fill in the file header
comments and add comments stating the question and any additional information needed. For
example:
% Question 1: Query to find movies released in 2006
% …
% Question 2: …
…
… and so on …
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Part 2: Basic Functions. For this part, you must implement and provide unit tests in Prolog for
each of the 10 functions specified in HW-7 (see HW-7 for details of each function). Each function
and your unit tests should go in hw10b.pl. To run your tests from the comman line, use:
$ swipl -g run_tests -t halt hw10b.pl
You can also run swipl, consult hw10b.pl, and then type run_tests from the query prompt.
Additional details will be provided in Piazza. The following lists the structures that should be used
for the corresponding HW-7 function.
1. my_min(X,Y,M) where M is the minimum of X and Y.
2. my_median(X,Y,Z,M) where M is the median of the other three arguments.
3. my_triangle_area(Base,Height,Area)
4. my_circle_area(Radius,Area)
5. my_midpoint((X1,Y1), (X2,Y2), (X3,Y3)) where (X1,Y1) is the first coordinate, (X2,Y2)
is the second coordinate, and (X3,Y3) is the midpoint between the two.
6. my_manhattan_distance((X1,Y1), (X2,Y2), D) where (X1,Y1) is the first point, (X2,Y2)
is the second point, and D is the manhattan distance between them.
7. my_euclidean_distance((X1,Y1), (X2,Y2), D) where (X1,Y1) is the first point, (X2,Y2)
is the second point, and D is the euclidean distance between them.
8. my_range_sum(Start,End,Sum) where Start is the starting value, End is the ending value,
and Sum is the sum of the range.
9. my_gcd(X,Y,D) where X and Y are integer values and D is the greatest common divisor.
10. my_even(X) and my_odd(X). Note that unlike in OCaml, these rules can be written separately
(actually, they must be).
Finally, note that unit tests are placed in a separate “block” within your source code (as specified
in the starter code). For instance, the following is an example of how to define a my_max relation
and then corresponding unit tests.
% “function” definitions
my_max(X,Y,X) :- X >= Y.
my_max(X,Y,Y) :- Y > X.
… rest of “function” definitions” …
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% unit tests
:- begin_tests(all_tests).
test(my_max_1) :- my_max(1,2,2), !.
test(my_max_2) :- my_max(2,1,2), !.
test(my_max_3) :- my_max(1,1,1), !.
… rest of unit tests for “functions” …
:- end_tests(all_tests).
Note above that the tests end with a “cut” (i.e., the “!” operator). A cut tells Prolog not to
backtrack after it reaches the cut operator (i.e., we are “cutting” the rest of the branches from the
proof tree). If we didn’t include the cut, the testing framework would give a warning that more
answers might exist. (Technically, we should use the cut in the rules themselves, but using the cut
in the test is sufficient for this assignment). Be sure to provide enough test cases to ensure each
relation is working correctly.
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Part 3: List Functions. Similar to above, write the following Prolog versions of the list functions
below from HW-8 in the file hw10c.pl along with corresponding unit tests. Note that each of these
are recursively defined with multiple cases. Like with OCaml pattern matching, you must take care
to clearly distinguish the cases from each other (especially since Prolog cases don’t “shadow” each
other—all cases are tried—and no warnings are given regarding shadowing).
1. The my_last function as the relation my_last(Xs,X) where X is the last element of the list
Xs.
2. The my_init function as the relation my_init(Xs,Ys) where the list Ys contains all but the
last element of the list Xs.
3. The my_replace function as the relation my_replace((A,B),Xs,Ys) where occurrences of A
in the list Xs are being replace by B in Ys.
4. The my_elem_sum function as the relation my_elem_sum(X,Ys,Sum) where X is the element
we want to add up in the list Ys to get the sum in Sum.
5. The my_min function as the relation my_min(Xs,M) where M is the minimum value in the list
Xs.
Be sure to provide enough test cases to ensure each relation is working correctly.
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Homework Submission. All homework must be submitted through GitHub Classroom. A link
for each assignment will be posted on Piazza when the homework is assigned. Be sure all of your
code is pushed by the due date (which you can double check for your repository using the GitHub
website). Each programming assignment is worth 35 points. The points are allocated based on
the following.
• Correct and Complete (25 points). Your code must correctly and completely do the
requested tasks using the requested techniques. Note that for most assignments you will be
provided a partial set of test cases to help you determine a minimal level of correctness. If
your program fails any of the provided test cases you will only receive partial credit. Note
that passing the given test cases does not mean your work is complete nor correct. Your
assignment will also be graded with additional test cases (not provided to you) that will help
the graders determine the extent of your solution and your final score. Note that for C++
code, correctness also implies properly handling the creation and deletion of dynamic memory
(i.e., the absence of memory leaks).
• Evidence and Quality of Testing (5 points). As part of your homework assignments
you must develop additional test cases beyond those given to you to ensure your program is
correct and complete. These test cases must be turned in with your assignment. You will be
graded on the scope and quality of the additional test cases you provide.
• Formatting and Comments (5 points). Your code must be formatted consistently and
appropriately for the language used. For C++, you must follow the provided style guide (see
the course webpage).You must also comment your code and test cases, which at a minimum
must include a file heading (see examples provided), function comments, and meaningfully
selected variable, class, and function names. See the assignment for style guides in other
languages.
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