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.
Top comments (1)
forgot that MathJax expression xd. Did anyone know how to use LaTeX in dev.to?