The issue is "what is the type of an inline record"? Internally each inline record in a constructor declaration has its own type, so in particular two different records have distinct types. One way to think of it is that

type t = A of {i:int} | B of {i:int};;

is morally equivalent to

type t_internal_A = {i : int};;

type t_internal_B = {i : int};;

type t = A of t_internal_A | B of t_internal_B;;

And then (function (A e | B e) -> e.i) does not type-check either -- with the same error message. This comes from the fact that, in OCaml (unlike in SML), records are nominal, have an identity: declaring another record type with the same fields creates a new, incompatible type.

So the answer is: this is a natural, expected consequence of how inline records and how records work in OCaml.

On Thu, Dec 15, 2016 at 9:12 AM, Gabriel Mayr <gabriel.mayr@mail.de> wrote:

Hi,

I'm using utop version 1.19.3 (using OCaml version 4.03.0).

Using an named record in a type definition and afterwards match on multiple constructors works:

# type a = {i:int};;

#type t = A of a | B of a;;

# let x = A {i=10};;

# match x with
| A e | B e -> print_int e.i;;

Using an unnamed record in a type definition and afterwards match on multiple constructors does not work:

# type t = A of {i:int} | B of {i:int};;

# let x = A {i=10};;

# match x with
| A e | B e -> print_int e.i;;

"Error: The variable e on the left-hand side of this or-pattern has type t.A but on the right-hand side it has type t.B"

I don't know if this is behaviour of OCaml is desired or it's a fault.

Hope I could help you with this little hint.

Best regards,

Gabriel

FreeMail powered by mail.de - mehr Sicherheit, Seriosität und Komfort