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Learning Haskell with Chess

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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.

@German Haskellers: You may also have a look at the tex-files used for our student exercises, http://www.steffen-mazanek.de/dateien/projekte/hsChess-teaching-german.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
      ,
      Eq
      ,
      deriving
      )
  • list handling (boards will be represented by lists of lists)
  • special character
    '\n'
    ,
    putStr::String->IO ()

1.2 Tasks

  • Define data types that represent boards (
    Board
    ), squares (
    Square
    ), positions (
    Pos
    ), pieces (
    Piece
    , supported by
    PieceColor
    and
    PieceType
    ) and game states (
    State
    ).
    • Helium: Implement suited eq and show functions.
    • Haskell: Define/derive instances of
      Show
      and
      Eq
  • Implement a function
    prettyBoard::Board->String
    , 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 (
    initialBoard::Board
    ), test
    prettyBoard
    with
    initialBoard
    .
  • Implement a simple evaluation function
    evalBoard::Board->Int
    as the difference of material on board, for this purpose define a function
    valuePiece
    that maps pieces to their values (pawn->1, knight and bishop->3, queen->9, rook->5, king->"infinity"=1000).

2 Exercise 2 - move generator

2.1 Learning targets

  • list comprehension
  • stepwise refinement

2.2 Tasks

  • Define a function
    movePos::Pos->Pos->Board->Board
    such that
    movePos p1 p2 b
    moves the piece at p1 to p2 (overwrite the square at p2 with the square at p1 and delete p1). Do not check whether the move is valid at this stage. Hint: Define a function
    updateBoard
    first.

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
    play::Gametree->Int
    , that computes the value of a given game tree using the minimax Algorithm.
  • Implement the function
    doMove::State->State
    , that choses the (best) next state.