[Haskell-cafe] Instances and multiple inheritance

[Patrick Browne]

How do I make an instance of the Vehicles class below?

Thanks,
Pat


class  Containers x y where
 insert :: y -> x y -> x y
 remove :: y -> x y -> x y
 whatsIn :: x y -> [y]


instance Containers [] Char where
 insert y [] = y:[]
 insert y m  = y:m
 remove _ []                 = []
 remove x (y:ys) | x == y    = remove x ys
                 | otherwise = y : remove x ys
 whatsIn  = id


instance Containers [] Integer where
 insert y [] = y:[]
 insert y m  = y:m
 remove _ []                 = []
 remove x (y:ys) | x == y    = remove x ys
                 | otherwise = y : remove x ys

 whatsIn  = id


instance Containers [] [a] where
  insert x y = x:y

-- lists of lists
-- insert [1] [[3,6],[45]]





class Surfaces a b where
 put :: b -> a b -> a b
 takeOff :: b -> a b -> a b
 whatsOn :: a b -> [b]

instance Surfaces [] Integer where
 put y [] = y:[]
 put y m  = y:m
 takeOff _ []                 = []
 takeOff x (y:ys) | x == y    = takeOff x ys
                  | otherwise = y : takeOff x ys
 whatsOn  = id


class Contacts a b where
 attach :: b -> a b -> a b
 detach :: b -> a b -> a b
 whatsAt :: a b -> [b]


instance Contacts [] Integer where
 attach y [] = y:[]
 attach y m  = y:m
 detach _ []                 = []
 detach x (y:ys) | x == y    = detach x ys
                  | otherwise = y : takeOff x ys
 whatsAt  = id


class Paths a b c where
 move :: c -> a b c -> a b c
 origin, destination :: a b c -> b
 whereIs :: a b c -> c -> b


instance Paths (,) Integer Integer where
 --  `Integer -> (Integer, Integer) -> (Integer, Integer)'
 move  c (a,b)  =   (a+1,b+1)
 origin  (a,b) = a
 destination  (a,b) = b
 whereIs  (a, b) c = b

-- Test
--  move (1::Integer) (3::Integer,5::Integer)
--  origin (3::Integer,5::Integer)


class People p where

class HeavyLoads l where

class Surfaces w o => WaterBodies w o where
instance WaterBodies [] Integer where

class Containers h o => Houses h o where

class (Surfaces v o, Paths a b (v o)) => Vehicles v o a b where


-- I do not know how to make an instance of Vehicles
-- What seems to be the *obvious* does not work
-- instance Vehicles [] Integer (,) Integer Integer  where
-- Kind error: `Vehicles' is applied to too many type arguments
-- In the instance declaration for
--       `Vehicles [] Integer (,) Integer Integer'


This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie