- : unit = ()
type foo = ..
type foo += A | B of int
val is_a : foo -> bool = <fun>
type foo
Line 2, characters 0-20:
2 | type foo += A of int (* Error type is not open *)
    ^^^^^^^^^^^^^^^^^^^^
Error: Type definition foo is not extensible
type foo = private ..
Line 2, characters 12-20:
2 | type foo += A of int (* Error type is private *)
                ^^^^^^^^
Error: Cannot extend private type definition foo
type 'a foo = ..
Line 2, characters 0-29:
2 | type ('a, 'b) foo += A of int (* Error: type parameter mismatch *)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This extension does not match the definition of type foo
       They have different arities.
module type S = sig type foo = private .. type foo += A of float end
Line 7, characters 2-24:
7 |   type foo += B of float (* Error: foo does not have an extensible type *)
      ^^^^^^^^^^^^^^^^^^^^^^
Error: Type definition foo is not extensible
type foo = ..
module M :
  sig
    type foo += A of int | B of string
    type foo += C of int | D of float
    
  end
module type S =
  sig
    type foo += B of string | C of int
    type foo += D of float
    type foo += A of int
  end
module M_S : S
type 'a foo = ..
type _ foo += A : int -> int foo | B : int foo
val get_num : 'a foo -> 'a -> 'a option = <fun>
type 'a foo = .. constraint 'a = [> `Var ]
type 'a foo += A of 'a
Line 2, characters 10-11:
2 | let a = A 9 (* ERROR: Constraints not met *)
              ^
Error: This expression has type int but an expression was expected of type
         [> `Var ]
Line 2, characters 19-22:
2 | type 'a foo += B : int foo (* ERROR: Constraints not met *)
                       ^^^
Error: This type int should be an instance of type [> `Var ]
type foo = ..
module M : sig type foo += A of int end
val a1 : foo = M.A 10
module type S = sig type foo += private A of int end
module M_S : S
val is_s : foo -> bool = <fun>
Line 2, characters 9-17:
2 | let a2 = M_S.A 20 (* ERROR: Cannot create a value using a private constructor *)
             ^^^^^^^^
Error: Cannot create values of the private type foo
type foo = ..
module M : sig type foo += A1 of int end
type foo += A2 of int
type bar = ..
Line 2, characters 17-21:
2 | type bar += A3 = M.A1    (* Error: rebind wrong type *)
                     ^^^^
Error: The constructor M.A1 has type foo but was expected to be of type bar
module M : sig type foo += private B1 of int end
type foo += private B2 of int
Line 2, characters 17-21:
2 | type foo += B3 = M.B1  (* Error: rebind private extension *)
                     ^^^^
Error: The constructor M.B1 is private
Line 2, characters 16-23:
2 | type foo += C = Unknown  (* Error: unbound extension *)
                    ^^^^^^^
Error: Unbound constructor Unknown
module M : sig type foo = private .. type foo += A1 of int end
type M.foo += A2 of int
type 'a foo = ..
type 'a foo1 = 'a foo = ..
type 'a foo2 = 'a foo = ..
type 'a foo1 += A of int | B of 'a | C : int foo1
type 'a foo2 += D of int | E of 'a | F : int foo2
type +'a foo = ..
type 'a foo += A of (int -> 'a)
Line 2, characters 0-31:
2 | type 'a foo += B of ('a -> int)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: In this definition, expected parameter variances are not satisfied.
       The 1st type parameter was expected to be covariant,
       but it is injective contravariant.
Line 2, characters 0-39:
2 | type _ foo += C : ('a -> int) -> 'a foo
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: In this definition, expected parameter variances are not satisfied.
       The 1st type parameter was expected to be covariant,
       but it is injective contravariant.
type 'a bar = ..
Line 2, characters 0-32:
2 | type +'a bar += D of (int -> 'a) (* ERROR: type variances do not match *)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This extension does not match the definition of type bar
       Their variances do not agree.
module M : sig type exn += Foo of int * float | Bar : 'a list -> exn  end
module M :
  sig exception Bar : 'a list -> exn exception Foo of int * float end
exception Foo of int * float
exception Bar : 'a list -> exn
module M : sig type exn += Foo of int * float | Bar : 'a list -> exn  end
type foo = ..
type foo += Foo of int * int option | Bar of int option
val x : foo * foo = (Foo (3, Some 4), Bar (Some 5))
type foo += Foo of string
val y : foo * foo = (<extension>, Bar (Some 5))
exception Foo of int * int option
exception Bar of int option
val x : exn * exn = (Foo (3, Some 4), Bar (Some 5))
type foo += Foo of string
val y : exn * exn = (Foo (3, _), Bar (Some 5))
type foo = ..
type foo += Foo | Bar of int
val extension_name : 'a -> string = <fun>
val extension_id : 'a -> int = <fun>
val n1 : string = "Foo"
val n2 : string = "Bar"
val t : bool = true
val f : bool = false
val is_foo : 'a -> bool = <fun>
type foo += Foo
val f : bool = false
Exception: Invalid_argument "Obj.extension_constructor".
Exception: Invalid_argument "Obj.extension_constructor".