haskell-jp / questions #88

aDest = 
        M   <$ "M"   <* char '='
    <|> D   <$ "D"   <* char '='
    <|> MD  <$ "MD"  <* char '='

aDest = asum . map (<* char '=') $
            [ M   <$ "M"
            , D   <$ "D"
            , MD  <$ "MD"
            ]

​-- AtCoderPrelude.hs
​module AtCoderPrelude (readUVecLn, parseInt, otherfct) where
​​import Control.Monad.State.Strict (StateT, runStateT)
​​import qualified Data.ByteString as BS
​import qualified Data.ByteString.Char8 as BSC
​​import qualified Data.Vector.Unboxed as VU
​​import qualified Some.Random.Module as M
​​
​​-- | Given a parser, parse a whole input line and give a vector.
​​readUVecLn
​​  :: (VU.Unbox a)
​​  => Int                          -- ^ Expected maximum length 
​​  -> StateT BS.ByteString Maybe a -- ^ Parser
​​  -> IO (VU.Vector a)
​​readUVecLn len parser
​​  = VU.unfoldrN len (runStateT parser) <$> BS.getLine
​
​-- | Skip spaces and control chars, and parse an Int.
​parseInt :: StateT BS.ByteString Maybe Int
parse​Int = StateT
​  $ BSC.readInt . BS.dropWhile (< fromIntegral (fromEnum '!'))
​
​otherfct :: A -> Very -> Useful -> Function
​​otherfct = M.usefulFunction "SomeGoodString"

​-- Main.hs
​import AtCoderPrelude
​
​main :: IO ()	
​main = do
​  n <- readLn
​  vec <- readUVecLn n parseInt
​  print vec

​-- Merged.hs
​import qualified Control.Monad.State.Strict (StateT, runStateT) as M3a6f5d
​​import qualified Data.ByteString as M65a7e5
​import qualified Data.ByteString.Char8 as M47ef44
​​import qualified Data.Vector.Unboxed as M3266e4
​​
​​readUVecLn_M2346ed
​​  :: (M3266e4.Unbox a)
​​  => Int
​​  -> M3a6f5d.StateT M65a7e5.ByteString Maybe a
​​  -> IO (M3266e4.Vector a)
​​readUVecLn_M2346ed len parser
​​  = M3266e4.unfoldrN len (M3a6f5d.runStateT parser) <$> M65a7e5.getLine
​
​parseInt_M2346ed :: M3a6f5d.StateT M65a7e5.ByteString Maybe Int
parse​Int_M2346ed = M3a6f5d.StateT
​  $ M47ef44.readInt . M65a7e5.dropWhile (< fromIntegral (fromEnum '!')
​
​main :: IO ()
​main = do
​  n <- readLn
​  vec <- readUVecLn_M2346ed n parseInt_M2346ed
​  print vec

{-# LANGUAGE CPP #-}

#include "AtCoderPrelude.hs"

millisSinceEpoch :: UTCTime -> Int 
millisSinceEpoch =
    floor . (1e3 *) . nominalDiffTimeToSeconds . utcTimeToPOSIXSeconds

main :: IO ()                                                                                                                                                                                                                                 
main = do
  start <- millisSinceEpoch <$> getCurrentTime
  threadDelay $ 2 * 10 ^ 6 
  end <- millisSinceEpoch <$> getCurrentTime
  print . show $ (end - start)

  newtype Difference = Difference { unDifference :: Int }
    deriving stock (Eq, Ord, Bounded)
    deriving newtype (Enum, Show, Read, Num, Real, Integral)
    deriving (Semigroup, Monoid) via Sum Int

src\Numeric\YHSeq\V0201.hs:32:15: error:
    • Couldn't match representation of type 'Int'
                               with that of 'Sum Int'
        arising from the coercion of the method '<>'
          from type 'Sum Int -> Sum Int -> Sum Int'
            to type 'Difference -> Difference -> Difference'
      The data constructor 'base-4.12.0.0:Data.Semigroup.Internal.Sum'
        of newtype 'Sum' is not in scope
    • When deriving the instance for (Semigroup Difference)
   |
32 |     deriving (Semigroup, Monoid) via Sum Int
   |

{-# LANGUAGE DerivingVia                #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module A where

-- import           Data.Monoid (Sum) -- 同様のコンパイルエラー
import           Data.Monoid (Sum (Sum)) -- コンパイルできる

newtype Difference = Difference { unDifference :: Int }
  deriving stock (Eq, Ord, Bounded)
  deriving newtype (Enum, Show, Read, Num, Real, Integral)
  deriving (Semigroup, Monoid) via Sum Int

The data constructor ‘base-4.12.0.0:Data.Semigroup.Internal.Sum’
of newtype ‘Sum’ is not in scope