NOTE: bounded polymorphism
source link: https://dannypsnl.github.io/blog/2020/01/24/cs/note-bound-polymorphism/
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NOTE: bounded polymorphism
Bounded polymorphism refers to existential quantifiers(∃\exists∃), 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.
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