int * int vs (int * int) in OCaml sum type

Question

type foo = A of int * int | B of (int * int)

What is the difference between int * int and (int * int) there? The only dif

Answer 1

As already said, the constructor of A takes two int, whereas the constructor of B takes an ordered pair.

so you can write

let bar = A (1, 2)

or

let bar = B (1, 2)

or

let bar = (1, 2)
let baz = B bar

but you cannot write

let bar = (1, 2)
let baz = A bar

Moreover, in your pattern matching, you can still match the content of B as two int, but you cannot match the content of A as value bound to an ordered pair

let test_foo = function
  | A a -> a (* wrong *)
  | B (f, s) -> (f, s) (* ok *)