Magic constructor lookup

[JonathanStarup]

It seems that in Ocaml you can do this magic constructor lookup

module A = struct type mylist = MyCons of int | MyNil end
type mylist2 = MyCons of string

match A.MyCons 1 with
  | MyCons x -> x
  | MyNil -> 123

Note that this doesn't work (mylist2 doesn't have MyNil)

module A = struct type mylist = MyCons of int | MyNil end
type mylist2 = MyCons of string

let f x = match x with
  | MyCons x -> x
  | MyNil -> assert true

but this does work

module A = struct type mylist = MyCons of int
type mylist2 = MyCons of string

let f x = match x with
  | MyCons x -> x

where f has type mylist2 -> string

So it seems that they import the constructors IF the scrutinee has a known data type at the time of inference of the match.

[magnus-madsen]

What happens with pairs etc? What if you match on a pair of two types that both define MyFoo?

[magnus-madsen]

I guess I am still confused about how the resolution works-- when you match on a program variable x.

[JonathanStarup]

What happens with pairs etc? What if you match on a pair of two types that both define MyFoo?

id guess different parts of the tuple have different imports

But yes it seems pretty wild