hs-connect4

Contents

• Introduction
• Project Hierarchy
• Getting Started
• State Representation
• Initial State
• Goal States
• Actions
• Heuristics
• Testing
• Support
• FAQ
• Development
• License
• References

Introduction

This is an implementation of connect4 game in Haskell.

If you are gamer and want to play connect4 or if you are a developer that want to test a functional language like Haskell, this project is done using behavior driven development using hspec that let a better understanding of each function.

This is an example to learn and know what can be done with Haskell.

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Project Hierarchy

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Getting Started

Requirements

• Haskell
• matrix package

Installation

To install the requirements:

1. sudo apt install haskell-platform

To get the matrix library update your cabal package list (if needed) with cabal update and then use cabal install matrix, assuming that you already have Cabal installed.

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State Representation

Connect4 game has a fixed board of n columns by m rows, usually 7-columns x 6-rows. The pieces fall straight down, occupying the lowest available space within the column.

The sequence of moves is represented on the board by columns that behaves as a stack of checkers, this board is implemented by a matrix.

Example: for a 7-columns x 6-rows board, the following sequence of moves have been done:

• Player 1 column 4
• Player 2 column 5
• Player 1 column 4
• Player 2 column 4

┌               ┐
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 2 0 0 0 │
│ 0 0 0 1 0 0 0 │
│ 0 0 0 1 2 0 0 │
└               ┘ 

Every move should be validated against the restrictions on the board:

• Cannot drop in a column outside the defined columns
• Cannot drop in a row that is already filled

As the game has a fixed board the following can also be defined:

columns = 7
rows = 6
total_turns = columns x rows
players = 2
turns_per_player = total_turns / players

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Initial State

The representation of the sequence of moves starts with an empty board of size columns x rows.

For example 7 columns x 6 rows:

┌               ┐
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
└               ┘

If player 1 is going to be first then:

next_turn_player = 1

If player 2 is going to be first then:

next_turn_player = 2

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Goal States

The objective is to connect four of your checkers in a row while preventing your opponent from doing the same.[1]

Examples of winning states for player 1:

• Horizontal

┌               ┐
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 1 1 1 1 0 0 │
└               ┘

• Vertical

┌               ┐
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 1 0 0 0 │
│ 0 0 0 1 0 0 0 │
│ 0 0 0 1 0 0 0 │
│ 0 0 0 1 0 0 0 │
└               ┘

• Diagonal

┌               ┐
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 1 0 0 │
│ 0 0 0 1 x 0 0 │
│ 0 0 1 x x 0 0 │
│ 0 1 x x x 0 0 │
└               ┘

Where x represent a move from any player

• Diagonal

┌               ┐
│ 0 0 0 0 0 0 0 │
│ 0 0 0 0 0 0 0 │
│ 0 0 1 0 0 0 0 │
│ 0 0 x 1 0 0 0 │
│ 0 0 x x 1 0 0 │
│ 0 0 x x x 1 0 │
└               ┘

Where x represent a move from any player

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Actions

initiate_board :: Num a => Int -> Int -> Matrix a
initiate_board rows columns = zero rows columns 

is_valid_position :: Matrix a -> Int -> Bool
is_valid_position board column =

is_user_turn :: Matrix a -> Int -> Bool
is_user_turn next_turn_player player = (== next_turn_player)

update_board :: Matrix a -> Int -> Board_State
update_board board column = 

is_win_position :: Matrix a -> Int -> 
is_win_position board  last_column_played = 

drop_checker :: Board_state -> Int -> Int -> Bool
drop_checker board_state player column = 

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Heuristics

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Testing

$ stack build --test

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Support

Technical support is available in

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FAQ

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Development

If you want to contribute....

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License

See LICENSE file

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References

1. Wikipedia Connect Four
2. Solving Connect four: How to build a perfect AI

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