[Ur] Opaque ascription

[Ron de Bruijn]

28-03-12 14:30, Adam Chlipala :
> Ron de Bruijn wrote:
>> The Ur/Web module system doesn't support opaque ascription currently.
>> Is there a reason for that considering that the compiler
>> implementation makes fairly extensive use of this Standard ML feature?
>
> Can you explain more what you want (maybe with an example)? I would use
> the word "opaque" to describe the only signature ascription operator
> that Ur includes.
In Robert Harper's book 'Programming in Standard ML' in section 20.2 named 
'Opaque ascription' he uses the :> notation.

The : notation is used for transparent ascription in Standard ML (and I assume 
also in Ur/Web).

http://en.wikipedia.org/wiki/Standard_ML also explains this.

It seems that you are saying that Ur's : == SML's :>, but then why has SML's : 
been left out in Ur