[r6rs-discuss] [Formal] Requirement to detect circular lists
cowan at ccil.org
Tue Oct 3 10:20:23 EDT 2006
Shiro Kawai scripsit:
> And I think you are comparing somewhat different things in your
> last paragraph. If the future RnRS doesn't have mutable pairs,
> 'map' will never receive a circular lists in RnRS compliant code
> (since there's no such thing like a circular lists in RnRS world),
Not necessarily. For example, one might introduce a primitive
(circular p q), where q is some non-empty tail of p, that returns
a list that is linear from p to q and circular back to q. This
cannot be *implemented* without pair mutation, but it does not
*expose* pair mutation.
Si hoc legere scis, nimium eruditionis habes.
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