LEARNING OUTCOMES

Upon completion of this piece of coursework, a student will be able to: understand the functionality of Prolog predicates and express it in natural language; understand textual descriptions of predicates and design the corresponding Prolog programs; implement recursive predicates on lists consisting of complex terms; implement predicates exploiting the power of higher order built-in predicates; utilise procedural abstraction to decompose a complex predicate description into simpler ones and synthesise complex predicates by reusing already defined built-in or user-defined predicates; develop correct and well-documented programs on specific problems, and test them.

ASSESSMENT CRITERIA

Program correctness (code loads to Prolog with no warnings or error messages, correct use of recursion, procedural abstraction and built-ins, production of correct results for normal and boundary cases).

Proper code documentation and meaningful variable and predicate names.

Programming style (proper use of variable assignment, efficiency).

Explanation of the provided code and justification of design choices.

DETAILED DESCRIPTION

Description of ISOLA

This is a two-player game. You start with a 7´7 position board, which initially contains two pieces, one for each player. Both players (h for human and c for computer) flip a coin and whoever wins plays first. At each turn, a player can do two consecutive moves:

· Move one's own piece to a neighbouring position (horizontally, vertically or diagonally) that is empty (not crossed out).

· Remove any position from the board by crossing it out.

The looser is the player who cannot move its piece to a neighbouring position, i.e. the piece is isolated. There is no draw. The figure on the next page presents an instance of the game.

Aim of the Practical

The aim of this practical is to implement this game in Prolog. One player will be the human, and the other player will be the program, and in our case the computer always plays first. We are not concerned with the program being intelligent (at least not during this semester!) so the program will perform all its moves at random.

Questions

1. What does the predicate pp/1 do and how? Would it matter if the board elements were messed up (not in order)? Would it be possible to write a recursive predicate that does the same operation? Again, would the order of board elements matter?

2. Write Prolog code for the predicate in_position/3, which given a number and a list of items, returns the item that corresponds to the position indicated by the number. For example:

?- in_position (4, [a,b,c,d,e,f], X).

X = d

[10%]

3. As it stands now, next/4 finds the neighbouring positions vertically and horizontally. Can you complete it to make it work for diagonal neighbours?

4. As it stands now, computer always plays first. Can you modify the code, so that the human decides either who plays first or if the first player is to be chosen at random?

5. Write the definition of the predicate find_options/3, which given a position (X and Y coordinates) and a board, returns a list of all available neighbouring positions.

6. Consider the partial definition of select_one_to_move/3 predicate. It is implemented for player h but not for player c. Complete the definition so that player c selects in random an available position to move.

7. Write the definition of the predicate select_a_position_to_cross/3 predicate so that either player c or h selects an available position to cross out.

8. The board of the game could be represented by alternative notations. For example:

A list with 49 ordered places, i.e.:

board([-,-, ... -,-]).

A list of seven lists of seven items each, i.e.:

board([[-,-,-,-,-,-,-],...,[-,-,-,-,-,-,-]]).

A set of facts, i.e.

board((1,1),-).

board((2,1),-).

board((3,1),-).

...

board((7,7),-).

What would be the pros and cons of such representations, considering code complexity for list manipulation, ordering of list items, time and space efficiency, or any other factor you may think of?

9. This game could have variations in scale:

· It could be played in a smaller or bigger board, for example a 5´5 or a 11´11 board.

· There could be more than 2 players.

· It could be 3-dimensional

What changes, if any, would you perform in each of the above cases to the program in order to make it work?