To expand slightly on Jacques' answer. Record fields (and variant
constructors) must be explicitly exported, using the:
 
  type t = Foo.t = { bar : int }
 
syntax.
 
For example, the following version of your example works:
 
  module type HasType = sig
    type t = { innerRecordField: int }
  end
 
  module EchoModule (Input : HasType) : HasType with type t = Input.t = struct
    type t = Input.t = {innerRecordField: int}
  end
 
  module ClonedModuleWithRecordType = EchoModule(struct
    type t = {innerRecordField: int}
  end)
 
  let myRecord: ClonedModuleWithRecordType.t = {
    ClonedModuleWithRecordType.innerRecordField=10;
  }
 
Of course, the `EchoModule` functor can now only operate on modules
where the type t is defined as:
 
  type t = { innerRecordField : int }
 
Jacques' solution of giving the functor argument a name, and using that
name to access the field, is a much more flexible approach.
 
Regards,
 
Leo
 
On Sun, 10 May 2015, at 05:58 PM, Jordan W wrote:
I believe there is an issue with record fields and functors.
It appears that while types are correctly exported from functors, the corresponding record field scopes are not. Here is an example.
 
   module type HasType = sig
      type t
    end
 
    module EchoModule (Input:HasType): (HasType with type t = Input.t) = (struct
      type t = Input.t
    end)
 
    module ClonedModuleWithRecordType = EchoModule (struct
      type t = {innerRecordField: int}
    end)
 
    (* This doesn't type check, but I can't see why it shouldn't. Record fields'
       scopes should be reexported just like the types themselves.
 
      let myRecord: ClonedModuleWithRecordType.t = {
        ClonedModuleWithRecordType.innerRecordField=10;
      }
 
      In this case, the original "scope" of the record fields is "lost"
      because the record type was declared in an anonymous module expression.  I
      believe that it *should* be "lost" as it is, but then reexported as an
      identical type in the module returned from the functor (identically because
      of the "with constraint").
 
    *)
 
    module ClonedModuleWithNonRecordType = EchoModule (struct
      type t = string list
    end)
 
    (* This typechecks perfectly fine! Evidence that types are reexported, but not
       the "scope" of record labels *)
    let myRecord: ClonedModuleWithNonRecordType.t = ["asdf"; "fff"]
 
 
Is anyone aware of whether or not this issue is already being tracked?