[Haskell-beginners] Chessboard Module, opinions on…

28 Oct 2009

      I have just recently finished a 'ChessBoard' module that is meant to  
represent a chess board. I could use some opinions and/or suggestions  
on the module.

To give an example of how this can be used right now, and was my  
immediate goal, you can do this:

*ChessBoard> putStr $ cout defaultBoard
+----+----+----+----+----+----+----+----+
| RB | NB | BB | QB | KB | BB | NB | RB |
+----+----+----+----+----+----+----+----+
| PB | PB | PB | PB | PB | PB | PB | PB |
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    |
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    |
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    |
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    |
+----+----+----+----+----+----+----+----+
| PW | PW | PW | PW | PW | PW | PW | PW |
+----+----+----+----+----+----+----+----+
| RW | NW | BW | QW | KW | BW | NW | RW |
+----+----+----+----+----+----+----+----+

I have not determined exactly how I will be making moves, but the  
logic will not be in my program. I am going to be using a chess engine  
in another process (I haven't chosen a chess engine yet that works on  
both windows and mac through stdin/stdout).

The module itself follows, I appreciate any thoughts you might have.

module ChessBoard where

import Data.Sequence
import Data.Foldable
import Data.Maybe
import Data.List as List

class NiceLook a where
     cout :: a -> String

data Piece = Bishop | Rook | Knight | King | Queen | Pawn | NoPiece
     deriving (Show, Eq)

instance NiceLook Piece where
         cout Bishop = "B"
         cout Rook   = "R"
         cout Knight = "N"
         cout Queen  = "Q"
         cout Pawn   = "P"
         cout King   = "K"
         cout _      = " "

data Colour = Black | White | NoColour
     deriving (Show, Eq)

instance NiceLook Colour where
         cout Black = "B"
         cout White = "W"
         cout NoColour = " "

         -- error "..." might be useful

data Square = Square Piece Colour
     deriving (Show, Eq)

instance NiceLook (Square) where
         cout (Square p c) = (cout p) ++ (cout c)

data Row = Row (Seq Square)
     deriving (Show, Eq)

instance NiceLook (Row) where
         cout (Row s) = "|" ++ foldMap (\x -> " " ++ cout x ++ " |")  
s       -- thnx Saizan

makeRow n = case (List.length n) of
                 8 -> Row (fromList n)
                 _ -> error "Row is not 8 squares"

makeColouredSquares n c = makeRow $ map makeSquare (zip n (replicate 8  
c))

makeSquare (n,c) = Square n c

pawns = [Pawn, Pawn, Pawn, Pawn, Pawn, Pawn, Pawn, Pawn]
back = [Rook, Knight, Bishop, Queen, King, Bishop, Knight, Rook]
blank = [NoPiece, NoPiece, NoPiece, NoPiece, NoPiece, NoPiece,  
NoPiece, NoPiece]

data Board = Board (Seq Row)
     deriving (Show, Eq)

instance NiceLook (Board) where
     cout (Board c) = borderOutput ++ "\n" ++ (foldMap (\x -> cout x + 
+ "\n" ++ borderOutput ++ "\n") c)

defaultBoard = Board (makeColouredSquares back Black <|
                       makeColouredSquares pawns Black <|
                       makeColouredSquares blank NoColour <|
                       makeColouredSquares blank NoColour <|
                       makeColouredSquares blank NoColour <|
                       makeColouredSquares blank NoColour <|
                       makeColouredSquares pawns White <|
                       makeColouredSquares back White <| empty)

borderOutput = "+" ++ (List.foldr1 (++) $ replicate 8 "----+")

[Haskell-beginners] Chessboard Module, opinions on…

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