12. コンパイル可能だが実行時エラー
head :: [a] -> a
head [] = error “empty list”
head (x:_) = x
main :: IO ()
main = print $ head ([] :: Int)
#NGK2017B
13. そもそもコンパイルエラー
{-@ head :: { xs:[a] | len xs > 0 } -> a @-}
head :: [a] -> a
head [] = error “empty list”
head (x:_) = x
main :: IO ()
main = print $ head ([] :: Int)
#NGK2017B
14. そもそもコンパイルエラー
{-@ head :: { xs:[a] | len xs > 0 } -> a @-}
head :: [a] -> a
head [] = error “empty list”
head (x:_) = x
main :: IO ()
main = print $ head ([] :: Int)
#NGK2017B