MATHFUN
Discrete Mathematics and Functional Programming
Functional Programming Assignment 2017/18 Introduction
This assignment aims to give you practice in using the constructs and techniques covered in the functional programming lectures and practicals by developing a complete Haskell program. This work will be marked out of 67 and carries 67% of the functional program- ming coursework mark (it will be combined with the 33% given for the in-class test held in January 2018).
You need to submit your program via the unit’s Moodle site by the deadline of 10pm, Monday 19th March 2018, and are required to demonstrate your program between 21st and 23rd March 2018. You will need to sign up for a demonstration time on a Google spreadsheet, the link for which will be distributed via email. All marks will be allocated in the demonstrations, so you must attend. If you miss your demonstration, it is your respon- sibility to arrange an alternative demonstration with me. If you submit or demonstrate your work late, your mark for this assignment will be capped according to CAM rules. Feedback and the mark for this assignment will be returned to you via email.
Your task
Your task is to write a program in Haskell for a film ratings website that lets users add films and display the details of various films. Users may also rate any film by saying they ‘like’ or ‘dislike’ it. A film’s ‘web-site rating’ is the percentage of its user ratings that are ‘likes’, rounded to the nearest whole number (for example, if a film has two likes and one dislike, its website rating is 67%). A film cannot have more than one rating from each user, but users can change their minds, for example, to like a film that they previously disliked. The site maintains a “database” (a textfile) of many films; each record of which gives a film’s title, the director, the year of release, a list of users who like the film, and a list of users who dislike the film.
Core functionality [32 marks]
The program should include pure (non-I/O) Haskell code that performs the following:
- add a new film to the database
- give all films in the database
- give all the films by a given director
- give all films that have a website rating of 75% or higher
- give the average website rating for the films of a given director
- give the titles of all films that a particular user has rated, along with how they have
been rated (‘like’ or ‘dislike’) by that user
- allow a user to say they like or dislike a particular film
- give all the films released between two given years (inclusive), sorted in descending order of website rating
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Each operation is worth 4 marks. Note that for operations (ii), (iii), (iv) and (viii), the well-formatted string-valued results should include each film’s title, director, year of release and website rating (but not the users’ ratings). The result for item (v) should be given to one decimal place.
You should begin by developing purely functional code to cover this core functionality, and then add to this the functions/actions that will comprise the program’s user interface. You may assume that no two films have the same title – i.e. any film can be uniquely identified by its title.
I recommend that you attempt the above items in order – the first few should be easier than those at the end. If you can’t complete all eight items of functionality, try to ensure that those parts that you have attempted are correct and as well-written as possible. Ensure also that every segment of code you write is appropriately documented.
Hints. Begin by copying and renaming the template.hs file from Moodle; your code should be developed within this file. Your first task will be to decide on a data representation Film for individual films. The database of films can then be of type [Film]. Now, for example, the functions to perform items (i) and (ii) above might have the types:
addFilm :: String -> String -> Int -> [Film] -> [Film] filmsAsString :: [Film] -> String
where addFilm title director year database returns a modified version of database with a new film (with the given title, director and year, and no likes or dislikes) added, and filmsAsString database gives a string which, when output using putStrLn, is well- formatted and multi-line. You may find it useful to define a few additional “helper” functions to aid in the writing of the program. You may also find functions in the Data.List and Text.Printf modules useful.
Test data. There is a file films.txt containing test data on Moodle. You should copy and edit this data so that it is a valid value of type [Film] given your particular Film type definition. Include this data in your program file as follows:
testDatabase :: [Film] testDatabase = [ ... the test data ... ]
to allow for easy testing as you develop the program’s functionality. It is this data that will be used to test your program in the in-class demonstration, so it is important that you include it fully and accurately. The in-class demonstration will make use of a demo function (the structure of which is supplied in the template.hs program). You should replace all the text in this function by corresponding expressions (this has essentially been done for you for demo 2). In the demonstration, if your user interface is missing or incomplete we will execute demo 1, demo 2 etc. to check your program. Make sure these expressions are working for all implemented functionality, or you will lose marks.
User Interface [15 marks]
Your program should provide a textual menu-based user interface to the above functional- ity, using the I/O facilities provided by Haskell. The user interface should be as robust as possible (it should behave appropriately given invalid input) and for those functions that
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give results, the display of these results should be well formatted. (This formatting should be handled by purely functional code, as detailed above.)
Your program should include a main function (of type IO ()) that provides a single starting point for its execution. When the program begins, the database should be loaded from a text-file, and all the films should be displayed (i.e. operation (ii) performed). It should then ask the user’s name; this name should then be used for functions (vi) and (vii). After the user enters their name, your program should present the menu for the first time.
Only when the user chooses to exit the program should the database be written back to this file (at no other times should files be used). Saving and loading can be implemented in a straightforward manner using the writeFile and readFile functions together with show and read (which convert data to and from strings).
Code quality [20 marks]
We will award marks based on your code’s completeness, readability and efficient use of Haskell’s functional programming and I/O facilities. Good use of powerful functional pro- gramming concepts (e.g. higher-order functions or list comprehensions) to achieve concise readable code will be rewarded.
Moodle submission
You should submit your program via the unit’s Moodle site by the deadline specified above. Make sure that your program file is named using your student number, and that it has a .hs suffix; for example, 123456.hs. Click on the link labelled “Haskell Assignment Submission” and upload your Haskell program. You should not upload your film database file.
Demonstration
You must not make changes to your program after submitting it to Moodle. You need to demonstrate the functionality of your copy of the program to us, and we may verify that this program is identical to the Moodle-submitted version. We may also ask you technical questions about the code in your program. Make sure that your database text-file includes an exact copy of the supplied test data at the time of the in-class demonstration to allow us to test the program’s correctness. If your user interface is not fully working it is vital that the demo function fully demonstrates the core functionality of your program: you will receive no credit for functionality that you cannot demonstrate with a user interface or the demo function. If your program gives unexpected results due to incorrect data in the database then you will lose marks.
Important
This is individual coursework, and so the work you submit for assessment must be your own. Any attempt to pass off somebody else’s work as your own, or unfair col- laboration, is plagiarism, which is a serious academic offence. Any suspected cases of plagiarism will be dealt with in accordance with University regulations.
Matthew Poole February 2018
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