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What does underscore mean in this type expression?
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Date: -- (:)
From: Christophe TROESTLER <Christophe.Troestler+ocaml@u...>
Subject: Re: [Caml-list] What does underscore mean in this type expression?
On Sat, 30 Aug 2008 14:03:10 +0100, Richard Jones wrote:
> 
> > # let x = ref `X;;
> > val x : _[> `X ] ref = {contents = `X}
> 
> OK ... so how to get rid of the error?  Even supplying a full type for
> get_domains in the implementation doesn't get rid of it.
> 
> Here's the code if anyone wishes to try:
> 
>   http://www.annexia.org/tmp/libvirt.mli
>   http://www.annexia.org/tmp/libvirt.ml
> 
>   $ ocamlc -c libvirt.mli
>   $ ocamlc -c libvirt.ml

Here is the crux of your problem

let f = let a = ref 0 in fun (x : [> `R ]) ->  x;;

If you hoist [let have_list_all_domains = ref None] outside [let
get_domains], then it works fine.  The type checker could certainly be
slightly improved [1] there but I do not know how difficult it is.

C.

---
[1] And maybe also the compiler: a rough check seem to indicate that
hiding the variable in the definition of f is slightly slower.