🚀 go-pugleaf

In article <BzDIL1.B4I@cs.uiuc.edu>, morrison@cs.uiuc.edu (Vance Morrison) writes:
> I have just realized something about ML that I find rather odd and 
> I am hoping to get some advice about consequences.
> 
> The oddity is that a value can escape the scope in which its type
> definition was made.   Thus
> 
> 
> 	let 
> 	   datatype aType = constA | constB of int;
> 	in
> 	   constA
> 	end;
> 
> 
> This of course returns the value 'constA', in the outer scope, but
> in this scope there is no type for this value!!
> 
> I tried this SML of NJ and it accepted it and returned the message
> 
> 		val it = constA : ?.aType
>  
> It seems to me that this can cause problem with the sematics of
> the language and would be a problem in any language that allows
> type definitions in inner scopes.  
> 
> Now my problem is that I don't know what the exact problems this 
> could cause, and I was hoping that those who have had more experience
> both defining and implementing ML could give their input.  
> 
> I have a copy of the Definition of ML, so if something there would
> make this clear, please feel free to refer to it.
> 
> Vance

Doesn't the "?.aType" mean that the object has a hidden type, ie a type inaccessible
in the current type environment. There is nothing you can actually do with the
returned value, so no problems should occur.

   .
   |on Hanson
 `-' jaxh@dcs.ed.ac.uk