# Learning Haskell with Chess

### From HaskellWiki

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===Learning targets=== |
===Learning targets=== |
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*recapitulate Haskell types (keywords type and data, product and sum types) |
*recapitulate Haskell types (keywords type and data, product and sum types) |
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− | **Helium: define equality functions (pattern matching) |
+ | **Helium: equality and show functions (pattern matching) |

− | **Haskell: define instances of type classes Show, Eq |
+ | **Haskell: type classes (<hask>Show</hask>, <hask>Eq</hask>, <hask>deriving</hask> |

*pretty printing |
*pretty printing |
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===Tasks=== |
===Tasks=== |
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− | *Define data types that represent boards (<hask>Board</hask>), squares (<hask>Square</hask>), positions (<hask>Pos</hask>), pieces (<hask>Piece</hask>) and game states (<hask>State</hask>). |
+ | *Define data types that represent boards (<hask>Board</hask>), squares (<hask>Square</hask>), positions (<hask>Pos</hask>), pieces (<hask>Piece</hask>, supported by <hask>PieceColor</hask> and <hask>PieceType</hask>) and game states (<hask>State</hask>). |

− | *Helium: Implement suited eq-functions. |
+ | **Helium: Implement suited eq and show functions. |

+ | **Haskell: Define/derive instances of <hask>Show</hask> and <hask>Eq</hask> |
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*Implement a function <hask>prettyBoard::Board->String</hask>, that transforms a board into a clearly arranged string representation (human readable :-)). Support this function with auxiliary functions that pretty print pieces, squares, ... |
*Implement a function <hask>prettyBoard::Board->String</hask>, that transforms a board into a clearly arranged string representation (human readable :-)). Support this function with auxiliary functions that pretty print pieces, squares, ... |
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*Define the initial board (<hask>initialBoard::Board</hask>), test prettyBoard with initialBoard. |
*Define the initial board (<hask>initialBoard::Board</hask>), test prettyBoard with initialBoard. |

## Revision as of 08:33, 19 March 2007

This page is about learning Haskell using the board game Chess as a running example. The complete code can be found at http://www.steffen-mazanek.de/dateien/projekte/hsChess.zip.

## Contents |

## 1 Exercise 1 - data types

### 1.1 Learning targets

- recapitulate Haskell types (keywords type and data, product and sum types)
- Helium: equality and show functions (pattern matching)
- Haskell: type classes (,Show,Eqderiving

- pretty printing

### 1.2 Tasks

- Define data types that represent boards (), squares (Board), positions (Square), pieces (Pos, supported byPieceandPieceColor) and game states (PieceType).State
- Helium: Implement suited eq and show functions.
- Haskell: Define/derive instances of andShowEq

- Implement a function , that transforms a board into a clearly arranged string representation (human readable :-)). Support this function with auxiliary functions that pretty print pieces, squares, ...prettyBoard::Board->String
- Define the initial board (), test prettyBoard with initialBoard.initialBoard::Board
- Implement a simple evaluation function as the difference of material on board (values: Pawn->1, Knight and Bishop->3, Queen->9, Rook->6, King->"infinity"=1000).evalBoard::Board->Int

## 2 Exercise 2 - move generator

### 2.1 Learning targets

- list comprehension
- stepwise refinement

### 2.2 Tasks

## 3 Exercise 3 - gametree generation and minimax algorithm

### 3.1 Learning targets

- break code in modules
- complexity
- recursive data structures -> recursive algorithms

### 3.2 Tasks

- Define a data type that represents a game tree ().GameTree
- Roughly estimate the number of nodes of the gametree with depth 4.
- Define a function , that computes the value of a given game tree using the minimax Algorithm.play::Gametree->Int
- Implement the function , that choses the (best) next state.doMove::State->State