Hello all,
I have found myself writing instances of Show for some types of
mine, and I did so by defining the showsPrec function, for performance
reasons. I ended up with code that I find quite inelegant. Here's
an example:
data Move = Move {
movePiece :: PieceType,
moveFile :: Maybe File,
moveTarget :: Square,
moveIsCapture :: Bool
--movePromotion :: Maybe PieceType
}
deriving (Eq)
instance Show Move where
showsPrec _
Move {
movePiece = p,
moveFile = f,
moveTarget = s,
moveIsCapture = c
} = (if p /= Pawn then shows p else id) .
(maybe id shows f) .
(if c then ('x':) else id) .
shows s
I considered writing a conditional composiion combinator to avoid all
the 'if foo then f else id' code. Something looking like this:
f .? True g = f . g
f .? False g = f
I'm not sure this is the best approach though, and I would be happy
to hear about your suggestions for improving the style of this code,
or any other comment that you think is appropriate.
Thanks,
Maxime
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