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NOTE: bounded polymorphism

Bounded polymorphism refers to existential quantifiers(∃), restricted to range over types of bound type. To understand it only needs a few examples. Let’s start! Take a look at the following program:

numSort :: Num a => [a] -> [a]

Num a is how we represent the bounded polymorphism in Haskell , the definition of Num was class Num b where(Hoogle shows a, just prevent to confuse reader don’t familiar with Haskell ) could read as a type b is an instance of class Num.

So numSort takes [a] only if a is an instance of Num. Now we could run down:

numSort [1, 2, 3] :: [Int]
numSort [1.1, 2, 3] :: [Double]

This is really a powerful feature(and you don’t need to use Haskell for this, Java also has this feature), consider the old way to do List<A> to List<B>, and unfortunately solution was to copy each element in the list.

Discussion (1)

dannypsnl profile image
林子篆 Author

forgot that MathJax expression xd. Did anyone know how to use LaTeX in