runtime/compile-time

gistfile1.hs

Prelude> class Pet a where kill :: a -> String
Prelude> data Dog = Dog deriving Show
Prelude> data Cat = Cat deriving Show
Prelude> instance Pet Dog where kill = const "dead"
Prelude> instance Pet Cat where kill = const "c_1|dead> + c_2|alive>"
Prelude> map kill [Cat, Cat] -- диспетчеризация времени компиляции
["c_1|dead> + c_2|alive>","c_1|dead> + c_2|alive>"]
Prelude> map kill [Dog, Dog] -- диспетчеризация времени компиляции
["dead","dead"]
Prelude> data PetBox where Box :: Pet a => a -> PetBox
Prelude> map (\(Box pet) -> kill pet) [Box Dog, Box Cat] -- динамическая диспетчеризация
["dead","c_1|dead> + c_2|alive>"]