Re: [Caml-list] Ocaml 4.02.0+dev4-2014-04-03 toplevel: module aliases no longer print module signature

[Leo White <lpw25@cam.ac.uk>]

The semantics of module aliases has changed in 4.02, so now:

    module S = String

creates a proper alias to String. This means, for example, that the type
`Map.Make(String).t` is now equivalent to `Map.Make(S).t`:

            OCaml version 4.02.0+dev4-2014-04-03

    # module S = String;;
    module S = String
    # let f (x : 'a Map.Make(String).t) : 'a Map.Make(S).t = x;;
    val f : 'a Map.Make(String).t -> 'a Map.Make(S).t = <fun>

where as previously:

            OCaml version 4.01.0
    # module S = String;;
    module S :
      sig
        [...]
      end
    # let f (x : 'a Map.Make(String).t) : 'a Map.Make(S).t = x;;
    Characters 55-56:
      let f (x : 'a Map.Make(String).t) : 'a Map.Make(S).t = x;;
                                                             ^
    Error: This expression has type 'a Map.Make(String).t
           but an expression was expected of type 'a Map.Make(S).t

In order to expose such aliases in signatures, you can now write `module
S = String` in signatures as well as structures. This is why the output
from the top-level has changed: it is still printing the type of `S`,
but `S` now has type `= String`.

To help people who previously defined aliases to print a module's
contents, the `#show` directive has been added to the top-level:

    # #show module String;;
    module String :
      sig
        [...]
      end

Regards,

Leo

Berke Durak <berke.durak@gmail.com> writes:

> On Sun, Apr 27, 2014 at 09:18:26AM -0400, Yaron Minsky wrote:
>> Sends preferable behavior to me, since it avoid overly long signatures and
>> more clearly reflects the new semantics of module aliases.
>
> If that's the issue, when the toplevel is connected to a tty, it should cut the
> output at some point and put an ellipsis.  If it's not a tty, it should still
> blast the full signature.
>
> I'm surely not the only one who has been relying on module X = Blah to see the
> signature of a module.  Old habits die hard.
>
> Also module SM = Map.Make(String) still prints the full declaration.
>
>> But it might be nice to have a way to see the contents of a module in the
>> toplevel.  Maybe steak the #typeof declaration from utop?
>
> How does one print a module signature in utop?
>
> -- 
> Berke Durak