instance overlap in 6.6 candidate

[Brian Smith]

On 9/5/06, Simon Peyton-Jones <simonpj at microsoft.com> wrote:
>
>
> The old model was that every instance is potentially overlappable; and
> you only need the flag when you *use* the instances.  But people
> complained that the clients of their library should not need to know
> "import Foogle and use -fallow-overlapping-instances".


I think that any module that depends on this feature in any way should
require the flag.

Foogle might define some overlapping instances which are meant to be used
only in its implementation--that is, users of Foogle aren't meant to make
use those instance declarations. In that scenario, I could see a case for
not requiring importing modules to specify the flag. But, I think that
depends on a mechanism for controlling whether or not an instance
declaration get exported in order to be useful.

- Brian
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