Re: [Caml-list] Re: Void type?

[Arnaud Spiwack <arnaud.spiwack@gmail.com>]

Jon Harrop a écrit :
> On Sunday 29 July 2007 12:05:47 Arnaud Spiwack wrote:
>   
>> It is the good solution if you work with the original syntax (and it's
>> absolutely equivalent to the dual definition in term of empty variant
>> which you can write in the revised syntax).
>>     
>
> I don't quite understand this "empty variant from the revised syntax thing". 
> How is:
>
>   type void
>
> not an empty variant?
>
>   
Well, not technically I believe. It's a type with no definition. I 
wouldn't be adamant about that but I reckon it's not considered as a sum 
type by OCaml type system.
Plus you cannot write the empty matching :
       match x with []
in the original syntax, preventing you from writing a function of type 
void -> 'a  without using exceptions or Obj.magic or an obviously 
looping function or such.

Thus it does not really have the logical behavior of an empty variant.




Arnaud Spiwack