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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.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.

1 Exercise 1 - data types

1.1 Learning targets

type
and
data
, product and sum types)
• Helium: equality and show functions (pattern matching)
Show
,
Eq
,
deriving
)
• list handling (boards will be represented by lists of lists)
• special character
'\n'
,
putStr::String->IO ()

• 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.
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

• 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. On top of this further define a function
deleteSquare
. 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
and
genMoves
to a function
nextStates::State->[State]
that returns all possible successor states.

3 Exercise 3 - gametree generation and minimax algorithm

3.1 Learning targets

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