Difference between revisions of "Learning Haskell with Chess"
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−  This page is about learning Haskell using the board game Chess as a running example. The source code can be found at [http://www.steffenmazanek.de/dateien/projekte/hsChess.zip]. 

+  olodom 

+  [[Category:Education]] 

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

−  <h1>Exercise 1  Data Types</h1> 

+  @German Haskellers: You may also have a look at the texfiles used for our student exercises, http://www.steffenmazanek.de/dateien/projekte/hsChessteachinggerman.zip. 

−  <h2>Learning Targets</h2> 

+  ==Exercise 1  data types== 

−  <ul> 

−  <li>recapitulate Haskell types (keywords type and data, product and sum types)</li> 

−  <li>Helium: define equality functions (pattern matching)</li> 

−  <li>pretty printing</li> 

−  </ul> 

−  <h2>Tasks</h2> 

+  ===Learning targets=== 

−  <ul> 

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

−  <li>Define data types that represent boards (Board), squares (Square), positions (Pos), pieces (Piece) and game states (State).</li> 

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

−  <li>Helium: Implement suited eqfunctions.</li> 

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

−  <li>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, ...</li> 

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

−  <li>Define the initial board (initialBoard::Board), test prettyBoard with initialBoard.</li> 

+  *special character <hask>'\n'</hask>, <hask>putStr::String>IO ()</hask> 

−  <li>Implement a simple evaluation function evalBoard::Board>Int as the difference of material on board (values: Pawn>1, Knight and Bishop>3, Queen>9, Rook>6, King>"infinity"=1000).</li> 

−  </ul> 

−  <h1>Exercise 2  Move Generator</h1> 

+  ===Tasks=== 

−  <h2>Learning Targets</h2> 

+  *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>). 

−  <h2>Tasks</h2> 

+  **Helium: Implement suited eq and show functions. 

+  **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, ... 

+  *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, 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). 

−  <h1>Exercise 3  Gametree Generation and Minimax Algorithm</h1> 

+  ==Exercise 2  move generator== 

−  +  ===Learning targets=== 

−  +  *list comprehension 

−  +  *stepwise refinement 

−  +  ===Tasks=== 

−  < 
+  *Define a function <hask>movePos::Pos>Pos>Board>Board</hask> such that <hask>movePos p1 p2 b</hask> 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 <hask>updateBoard</hask> first. On top of this further define a function <hask>deleteSquare</hask>. Its much simpler to have these functions at hand. 
−  </ 
+  *Implement a function <hask>colorPos::PieceColor>Board>[Pos]</hask> whose result is the list of the positions of the pieces of a certain color. 
−  < 
+  *Define <hask>moves::PieceType>[(Int,Int)]</hask> that returns the base moving vectors for a particular piece (return empty list for pawns here, because their vector depends on the color). 
−  < 
+  *Implement <hask>genMoves::Board>Pos>[Board]</hask>, it takes a board b and a position p and results in the list of all boards that may follow if you move the piece at p on board b. 
−  < 
+  *Combine <hask>colorPos</hask> and <hask>genMoves</hask> to a function <hask>nextStates::State>[State]</hask> that returns all possible successor states. 
−  +  
−  +  ==Exercise 3  gametree generation and minimax algorithm== 

−  +  ===Learning targets=== 

−  +  *break code in modules 

+  *complexity 

+  *recursive data structures > recursive algorithms 

+  
+  ===Tasks=== 

+  *Define a data type that represents a game tree (<hask>GameTree</hask>). 

+  *Roughly estimate the number of nodes of the gametree with depth 4. 

+  *Define a function <hask>play::Gametree>Int</hask>, that computes the value of a given game tree using the minimax Algorithm. 

+  *Implement the function <hask>doMove::State>State</hask>, that choses the (best) next state. 
Latest revision as of 22:54, 5 October 2008
olodom This page is about learning Haskell using the board game Chess as a running example. The complete code can be found at http://www.steffenmazanek.de/dateien/projekte/hsChess.zip.
@German Haskellers: You may also have a look at the texfiles used for our student exercises, http://www.steffenmazanek.de/dateien/projekte/hsChessteachinggerman.zip.
Contents
Exercise 1  data types
Learning targets
 recapitulate Haskell types (keywords
type
anddata
, 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 ()
Tasks
 Define data types that represent boards (
Board
), squares (Square
), positions (Pos
), pieces (Piece
, supported byPieceColor
andPieceType
) and game states (State
). Helium: Implement suited eq and show functions.
 Haskell: Define/derive instances of
Show
andEq
 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
), testprettyBoard
withinitialBoard
.  Implement a simple evaluation function
evalBoard::Board>Int
as the difference of material on board, for this purpose define a functionvaluePiece
that maps pieces to their values (pawn>1, knight and bishop>3, queen>9, rook>5, king>"infinity"=1000).
Exercise 2  move generator
Learning targets
 list comprehension
 stepwise refinement
Tasks
 Define a function
movePos::Pos>Pos>Board>Board
such thatmovePos 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 functionupdateBoard
first. On top of this further define a functiondeleteSquare
. Its much simpler to have these functions at hand.  Implement a function
colorPos::PieceColor>Board>[Pos]
whose result is the list of the positions of the pieces of a certain color.  Define
moves::PieceType>[(Int,Int)]
that returns the base moving vectors for a particular piece (return empty list for pawns here, because their vector depends on the color).  Implement
genMoves::Board>Pos>[Board]
, it takes a board b and a position p and results in the list of all boards that may follow if you move the piece at p on board b.  Combine
colorPos
andgenMoves
to a functionnextStates::State>[State]
that returns all possible successor states.
Exercise 3  gametree generation and minimax algorithm
Learning targets
 break code in modules
 complexity
 recursive data structures > recursive algorithms
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.