6
Type Classes
Like most other programming languages, Haskell features a number of overloaded operators and functions, such as (+), that work at different types. For instance, (+) has the following four types:
(+) :: Int -> Int -> Int (+) :: Integer -> Integer -> Integer (+) :: Float -> Float -> Float (+) :: Double -> Double -> Double
Overloading is not the same as (parametric) polymorphism: (+) does not have the type a -> a -> a and does not work on all possible types. Overloading means that the operator only works for a specific set of types and that the operator’s behavior is different for each type.
In many languages, overloading is ad hoc: it exists for a fixed number of operators and functions and a fixed set of types. Moreover, a function ...
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