haskelltuplestype-constructor

What is the type constructor for list of tuples?


The question

What is the type constructor which generates a concrete type like [(Int,String)]?

The origin of the question

I think this really sounds either like a stupid question or a meaningless riddle. I hope the following convinces you that I'm actually trying to find gaps in my understanding of the basics.

I know that []

to "visualize" the second aspect, I can just type

> x = [1,2,3] :: [] Int
> :t x
x :: [Int]

which clearly shows that [] applied to the concrete type Int gives another concrete type [Int].

So far so good.

On the other hand, (,) also has two meanings:

> x = (1,1) :: (,) Int Int
> :t
x :: (Int, Int)
> (,) 1 "hello"
(1,"hello")

So, if both [] and (,) are type constructors that can originate, among other types, concrete types [Int] and (Int,Char), I wonder what is the type constructor that generates a type like [(Int,Char)].


Solution

  • It's not so much a single type constructor as it is a nested type constructor:

    λ> x = [(1, 'a')] :: [] ((,) Int Char)
    λ> :t x
    x :: [(Int, Char)]