On Dec 14, 2010, at 19:11, Russ Abbott wrote:
I'm also confused about how to do the equivalence of inheritance in Haskell. Here is a complete example below. It doesn't compile. The error message is
Class `Person' used as a type
If I write "(Person p) =>" instead, I get other diagnostics.
I would very much appreciate seeing how this should be done in Haskell.
What about
---------- Example (multiple files) ------------ --- Group.hs --- module Group where
import Person
data Group = Group { members :: [Person] }
instance Show Group where show group = unlines $ map show $ members group
--- Person.hs ---
module Person where
data Person = Person { nameP :: p -> String , ageP :: p -> Int , getGenderSpecificCondition :: p -> Condition }
instance Show Person where show p = nameP p ++ "(" ++ show (ageP p) ++ ", " ++ show (getGenderSpecificCondition p) ++ ")"
data Condition = Bad | OK | Good
class PersonClass p where toPerson :: p -> Person
--- Man.hs --- module Man where
import Person
data Man = Man { nameM :: String , ageM :: Int , prostateCondition :: Condition }
instance PersonClass Man where
toPerson (Man n a c) = Person n a c
--- Woman.hs--- module Woman where
import Person
data Woman = Woman { nameW :: String , ageW :: Int , ovaryCondition :: Condition }
instance Person Woman where
toPerson (Woman n a c) = Person n a c
---------- End example (multiple files) ------------