Re: datatype constructor as syntax

19/03/14 23:37, Phil Clayton wrote:
> 19/03/14 19:16, Matthew Fluet wrote:
>> On Tue, Dec 31, 2013 at 3:47 AM, Florian Weimer <[email protected]> wrote:
>>> * Henry Cejtin:
>>>
>>>> Sorry,  I  thought  I  was  being  clever,  but  if  you look at Andreas
>>>> Rossberg's Defects in the Revised Definition of Standard ML
>>>>       http://www.ps.uni-saarland.de/Publications/documents/Rossberg_DefectsSML.pdf
>>>> you will see that he points out that rule 126 of the  dynamic  semantics
>>>> implies  that  this  should really give you a bind exception at runtime.
>>>> This was fixed (meaning you get the in MLton way back in 2001 to give an
>>>> error at compile time.
>>>
>>> Curiously, the fun-based approach
>>>
>>>     datatype mytype = foo | bar of int
>>>     fun bar _ = ()
>>>     val bar = 23
>>>
>>> still runs without raising an exception when compiled with MLton.
>>
>> That seems to be an oversight.
>
> Perhaps I missed the point here but I'm hoping that it's intentional
> that MLton allows the status of a constructor id to be overwritten by a
> fun binding.  I am relying on code as follows to create a value NONE:
>
>     local
>       fun NONE () = <expression>
>     in
>       val NONE = NONE ()
>     end
>
> Note that this does not create an unreferenced id, which avoids spurious
> warnings from such checks, for example, using Poly/ML with
>     PolyML.Compiler.reportUnreferencedIds := true;
>
> If this isn't allowed, how should a value called NONE be created?

Responding to myself:

   local
     structure S : sig val NONE : int option end = struct open Option end
     open S
   in
     val NONE = <expression>
   end

Yuk!  Is there anything nicer?

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