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{-# LANGUAGE TemplateHaskell #-}
module Issue23 (test) where
import Data.Functor.Identity
import Data.Functor.Classes
import qualified Rank2
import qualified Rank2.TH
import Test.Tasty (TestTree)
import Test.Tasty.HUnit (testCase, assertEqual)
data Stm r = Unit | ExpStmt (r Int) (Exp r)
data Exp r = Nil | Cons (r Bool) (Exp r) (Stm r)
instance Show1 r => Show (Stm r) where
show Unit = "Unit"
show (ExpStmt r e) = "(Stmt (" ++ showsPrec1 0 r (") " ++ show e ++ ")")
instance Show1 r => Show (Exp r) where
show Nil = "Nil"
show (Cons r e s) =
"(Cons (" ++ showsPrec1 0 r (") " ++ show e ++ " " ++ show s ++ ")")
$(mconcat <$> traverse
(\derive -> mconcat <$> traverse derive [''Stm, ''Exp])
[ Rank2.TH.deriveFunctor
, Rank2.TH.deriveFoldable
, Rank2.TH.deriveTraversable
])
expToMaybe :: Exp Identity -> Exp Maybe
expToMaybe = Rank2.fmap (Just . runIdentity)
maybeToExp :: Exp Maybe -> Maybe (Exp Identity)
maybeToExp = Rank2.traverse (fmap Identity)
myExp :: Exp Identity
myExp = Cons
(Identity True)
(Cons (Identity False) Nil (ExpStmt (Identity 2) Nil))
(ExpStmt (Identity 3) (Cons (Identity True) Nil Unit))
test :: TestTree
test = testCase "Issue #23" $ do
print myExp
let myExp' = expToMaybe myExp
assertEqual "" (show $ Just myExp) (show $ maybeToExp myExp')
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