In Haskell, the simplest way to check if a class has a method is to use the elem function. This function checks whether an element is in a list of elements or not. We can use the function in the following way:
elem "method_name" $ map show $ methods (undefined :: ClassName a)
Explanation of the code:
- methods is a function provided by the GHC.Generics module, which returns a list of all the method names of a class.
- map show converts the list of method names to a list of strings.
- undefined :: ClassName a creates an instance of the class with a type variable a. We don't care about this variable, we just need to have an instance of the class in order to call the methods function.
- "method_name" is the name of the method we want to check for.
- elem checks if "method_name" is present in the list of method names.
Here's an example:
import GHC.Generics
class MyFuncs a where
foo :: a -> a
bar :: a -> a -> a
classHasMethod :: String -> Bool
classHasMethod methodName = elem methodName $ map show $ methods (undefined :: MyFuncs a)
main :: IO ()
main = do
putStrLn $ "MyFuncs has method foo? " ++ show (classHasMethod "foo") -- True
putStrLn $ "MyFuncs has method baz? " ++ show (classHasMethod "baz") -- False
Here, we have defined a class MyFuncs with two methods foo and bar. We then define a function classHasMethod, which takes a method name as an argument and returns True if the class has that method, and False otherwise. Finally, we call classHasMethod for the method names foo and baz and print the results. The output will be:
MyFuncs has method foo? True
MyFuncs has method baz? False