The Paradox of Partial Parametricity

Andreas Rossberg rossberg at google.com
Fri May 10 12:39:25 PDT 2013


[+es-discuss]

On 10 May 2013 21:05, Andreas Rossberg <rossberg at google.com> wrote:
> On 10 May 2013 14:52, Mark S. Miller <erights at google.com> wrote:
>> An upper case type variable, e.g. T, is fully parametric. It may be a
>> promise or non-promise.
>> A lower case type variable, e.g. t, is constrained to be a non-promise. If
>> you wish to think in conventional type terms, consider Any the top type
>> immediately split into Promise and non-promise. Thus type parameter t is
>> implicitly constrained to be a subtype of non-promise.
>
> Mark, I'm afraid such a distinction makes absolutely no sense in a
> world of structural types. How would you specify the set of "types
> that aren't promises" in a way that is compatible with structural
> subtyping?
>
> /Andreas


More information about the es-discuss mailing list