Haskell: Deriving Show for custom type

Question

I have this type definition:

data Operace = Op (Int->Int->Int) String (Int->Int->Int) deriving Show 

I want to print this type into the interactive shell (GHCi). All that should be printed is the String field.

I tried this:

instance Show Operace where     show (Op op str inv) = show str 

But I still keep getting

No instance for (Show (Int -> Int -> Int))   arising from the 'deriving' clause of a data type declaration Possible fix:   add an instance declaration for (Show (Int -> Int -> Int))   or use a standalone 'deriving instance' declaration,        so you can specify the instance context yourself When deriving the instance for (Show Operace) 

I don't want to add Show for (Int->Int->Int), all I want to print is the string.

Thanks for help!

EDIT:

For future reference, the fixed version is:

data Operace = Op (Int->Int->Int) String (Int->Int->Int)  instance Show Operace where     show (Op _ str _) = str 

Answer 1

The instance declaration you made is the correct way to go. It seems you forgot to remove that faulty deriving clause from the original data declaration.

data Operace = Op (Int->Int->Int) String (Int->Int->Int)  instance Show Operace where    show (Op op str inv) = show str 

Answer 2

You can derive Show, just import Text.Show.Functions first.