52 lines
1.6 KiB
Haskell
52 lines
1.6 KiB
Haskell
--------------------------------------------------------------------------------
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module Transforms where
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--------------------------------------------------------------------------------
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import Control.Applicative ((<|>))
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import Text.ParserCombinators.ReadP
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--------------------------------------------------------------------------------
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data Transform = VerticalFlip
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| HorizontalFlip
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| Shift Int
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deriving (Eq, Show)
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digit :: ReadP Char
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digit =
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satisfy (\c -> c >= '0' && c <= '9')
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command :: ReadP Transform
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command = vertical
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<|> horizontal
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<|> shift
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where
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vertical =
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char 'V' >> pure VerticalFlip
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horizontal =
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char 'H' >> pure HorizontalFlip
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shift = do
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_ <- char 'S'
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negative <- option Nothing $ fmap Just (satisfy (== '-'))
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n <- read <$> many1 digit
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case negative of
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Nothing -> pure $ Shift n
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Just _ -> pure $ Shift (-1 * n)
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-- | Attempt to remove redundant transformations.
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-- | Here are some rules that I'd like to support but may not have time for:
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-- | - All even-numbered flips (w/o intermittent shifts) can become zero
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-- | - All odd-numbered flips (w/o intermittent shifts) can become 1
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-- | - All shifts can be be reduce to the absolute value of shifts
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optimize :: [Transform] -> [Transform]
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optimize [] = []
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optimize [x] = [x]
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optimize (VerticalFlip:VerticalFlip:xs) = optimize xs
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optimize (HorizontalFlip:HorizontalFlip:xs) = optimize xs
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optimize xs = xs
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fromString :: String -> Maybe [Transform]
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fromString x =
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case readP_to_S (manyTill command eof) x of
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[(res, "")] -> Just res
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_ -> Nothing
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