Changes to Typeable

Ben Millwood haskell at
Wed Oct 3 23:25:32 CEST 2012

On Wed, Oct 3, 2012 at 9:26 PM, Robin KAY <komadori at> wrote:
> On 03/10/12 14:20, Edward Kmett wrote:
>> I don't think anyone has proposed weakening parametricity in this way.
> [snip]
> I don't think so either, but is there any reason it shouldn't be done?

Uh, because it weakens parametricity? :) Free theorems would promptly
vanish, since we would have effectively added typecase to the
language: it would no longer be possible to conclude from a type
signature a -> a that the function was the identity, for example.

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