haskell-jp / general #1

data (Show a) => Color a = Red | Green | Blue | Rgb {r :: a, g :: a, b :: a} deriving (Show)

data (Show a) => Color a where
  Red :: Color
  Green :: Color
  Blue :: Color
  Rgb :: {r ::a, g :: a, b :: a} -> Color
  deriving (Show)

data Color a where
  Red :: Color
  Green :: Color
  Blue :: Color
  Rgb :: (Show a) => {r ::a, g :: a, b :: a} -> Color
  deriving (Show)

{-# LANGUAGE GADTs #-}
data Color a where
  Red :: Color
  Green :: Color
  Blue :: Color
  Rgb :: (Show a) => {r ::a, g :: a, b :: a} -> Color
  deriving (Show)
main = print (Red :: (Color Integer))

prog.hs:3:10: error:
    • Expecting one more argument to ‘Color’
      Expected a type, but ‘Color’ has kind ‘k0 -> *’
    • In the type ‘Color’
      In the definition of data constructor ‘Red’
      In the data declaration for ‘Color’
  |
3 |   Red :: Color
  |          ^^^^^

data Color a where
  Red :: Color a
  Green :: Color a
  Blue :: Color a
  Rgb :: (Show a) => {r ::a, g :: a, b :: a} -> Color a
  deriving (Show)
main = print (Red :: (Color Integer))

prog.hs:7:13: error:
    • Can't make a derived instance of ‘Show (Color a)’:
        Constructor ‘Rgb’ has constraints in its type
        Possible fix: use a standalone deriving declaration instead
    • In the data declaration for ‘Color’
  |
7 |   deriving (Show)
  |    

{-# LANGUAGE GADTs #-}
data (Show a) => Color a where
  Red :: Color a
  Green :: Color a
  Blue :: Color a
  Rgb :: {r ::a, g :: a, b :: a} -> Color a
  deriving (Show)
main = print (Red :: (Color Integer))

{-# LANGUAGE GADTs #-}
data Color a where
  Red :: (Show a) => Color a
  Green :: (Show a) => Color a
  Blue :: (Show a) => Color a
  Rgb :: (Show a) => {r ::a, g :: a, b :: a} -> Color a
  deriving (Show)
main = print (Red :: (Color Integer))

prog.hs:7:13: error:
    • Can't make a derived instance of ‘Show (Color a)’:
        Constructor ‘Red’ has constraints in its type
        Constructor ‘Green’ has constraints in its type
        Constructor ‘Blue’ has constraints in its type
        Constructor ‘Rgb’ has constraints in its type
        Possible fix: use a standalone deriving declaration instead
    • In the data declaration for ‘Color’
  |
7 |   deriving (Show)
  |             ^^^^

data Color a = Red | Green | Blue | Rgb {r :: a, g :: a, b :: a}　deriving (Show)

{-# LANGUAGE GADTs, StandaloneDeriving #-}

data Color a where
  Red :: (Show a) => Color a
  Green :: (Show a) => Color a
  Blue :: (Show a) => Color a
  Rgb :: (Show a) => {r ::a, g :: a, b :: a} -> Color a

deriving instance Show (Color a)

main = print (Red :: (Color Integer))