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Datatypes

Parameterized types, type constructors​

  • In Haskell, many types are parameterized by others.
  • From existing types, we can make new types.
  • Parameterized types are often called type constructors.

Examples:

“List” is a type constructor.

Given any type a , there is also a type [a].

“Pair” is a type constructor.

Given any types a and b , there is also a type (a, b).

“Function” is a type constructor.

Given any types a and b , there is also a type a -> b.

Building types with type constructors There are no limits to composing type constructors:

([Int -> Bool -> Int], [[Double]] -> (Bool, Int))

There are arbitrarily many type constructors, because we can define our own!