# Learning Haskell with Chess

### From HaskellWiki

(Difference between revisions)

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===Learning targets=== | ===Learning targets=== | ||

− | *recapitulate Haskell types (keywords type and data, product and sum types) | + | *recapitulate Haskell types (keywords <hask>type</hask> and <hask>data</hask>, product and sum types) |

**Helium: equality and show functions (pattern matching) | **Helium: equality and show functions (pattern matching) | ||

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

− | * | + | *list handling (boards will be represented by lists of lists) |

===Tasks=== | ===Tasks=== | ||

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**Haskell: Define/derive instances of <hask>Show</hask> and <hask>Eq</hask> | **Haskell: Define/derive instances of <hask>Show</hask> and <hask>Eq</hask> | ||

*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, ... | ||

− | *Define the initial board (<hask>initialBoard::Board</hask>), test prettyBoard with initialBoard. | + | *Define the initial board (<hask>initialBoard::Board</hask>), test <hask>prettyBoard</hask> with <hask>initialBoard</hask>. |

− | *Implement a simple evaluation function <hask>evalBoard::Board->Int</hask> as the difference of material on board | + | *Implement a simple evaluation function <hask>evalBoard::Board->Int</hask> as the difference of material on board, for this purpose define a function <hask>valuePiece</hask> that maps pieces to their values (pawn->1, knight and bishop->3, queen->9, rook->5, king->"infinity"=1000). |

==Exercise 2 - move generator== | ==Exercise 2 - move generator== |

## Revision as of 08:39, 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 andtype, product and sum types)data
- Helium: equality and show functions (pattern matching)
- Haskell: type classes (,Show,Eq)deriving

- list handling (boards will be represented by lists of lists)

### 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 (), testinitialBoard::BoardwithprettyBoard.initialBoard
- Implement a simple evaluation function as the difference of material on board, for this purpose define a functionevalBoard::Board->Intthat maps pieces to their values (pawn->1, knight and bishop->3, queen->9, rook->5, king->"infinity"=1000).valuePiece

## 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