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module M
( mkB2
) where
import Control.Monad.Reader
import Data.Maybe
data A1 = A1 (Maybe String) (Maybe String) (Maybe String) (Maybe String)
data A2 = A2 A1 (Maybe String) (Maybe String) (Maybe String) (Maybe String)
(Maybe String) (Maybe String) (Maybe String) (Maybe String)
data B1 = B1 !String !String !String !String
data B2 = B2 !B1 !String !String !String !String !String !String !String !String
type M a = ReaderT [(String, String)] (Either String) a
resolve :: Maybe String -> String -> M (Maybe String)
resolve (Just x) _ = pure (Just x)
resolve Nothing v = asks $ lookup v
mkB1 :: A1 -> M B1
mkB1 (A1 a b c d) = do
a' <- fromMaybe "" <$> resolve a "A"
b' <- fromMaybe "" <$> resolve b "B"
c' <- fromMaybe "" <$> resolve c "C"
d' <- fromMaybe "" <$> resolve d "D"
pure $ B1 a' b' c' d'
mkB2 :: A2 -> M B2
mkB2 (A2 a b c d e f g h i) = do
a' <- mkB1 a
b' <- fromMaybe "db" <$> resolve b "B"
c' <- fromMaybe "dc" <$> resolve c "C"
d' <- fromMaybe "dd" <$> resolve d "D"
e' <- fromMaybe "de" <$> resolve e "E"
f' <- fromMaybe "df" <$> resolve f "F"
g' <- fromMaybe "dg" <$> resolve g "G"
h' <- fromMaybe "dh" <$> resolve h "H"
i' <- fromMaybe "di" <$> resolve i "I"
pure $ B2 a' b' c' d' e' f' g' h' i'
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