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How important are circular lists/recursive objects?
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Date: -- (:)
From: Andreas Rossberg <rossberg@m...>
Subject: Re: [Caml-list] Re: How important are circular lists/recursive objects?
skaller wrote:
>>> Note that stuff like:
>>>
>>> 	let rec x= (1,x)
>>>
>>> is not generally allowed: in functional terms it is ill-defined,
>>>       
>> It is disallowed in OCaml because it has a cyclic type, not because it is
>> a cyclic value. Try with "ocaml -rectypes".
>>     
>
> lists have cyclic types too, they're not disallowed!
>   

Technically speaking they haven't, because conventional variant types 
are nominal, not structural.

In any case, even OCaml without -rectypes allows some cyclic types (if 
the cycle goes through an object or polymorphic variant type), but not 
arbitrary ones. That is a pragmatic design decision to avoid too many 
bogus examples to type-check.

- Andreas