RFC: Singleton equality witnesses

[Iavor Diatchki]

Hello,

my preference would be to build this kind of functionality (and other
related features) in libraries on top of GHC.TypeLits.  This modules was
intended to contain only a minimal set of the constants that the compiler
needs to know about, and it already may have too much in it.

On the concrete issue:  orphan instances could be avoided if the type lits
instances are defined in the same module as the class.

-Iavor


On Thu, Feb 7, 2013 at 6:50 AM, Gabor Greif <ggreif at gmail.com> wrote:

> In its current state it is not tied to TypeLits, but when Richard adds
> his magic it probably will be. It is still an open issue where to put
> what, and whether a new module would be fitting.
> Richard surely will comment on this. I'd prefer the new instance
> definitions in TypeLits to avoid orphans. Thanks for your input
> though, this is exactly the kind of feedback we were hoping for :-)
>
> Cheers,
>
>     Gabor
>
>
> [looks like I lost a previous version of this response, sorry if you
> get it twice]
>
> On 2/7/13, José Pedro Magalhães <jpm at cs.uu.nl> wrote:
> > Hey Gabor,
> >
> > And why should it be part of base? Don't get me wrong, I'm not saying
> this
> > is not important/useful. I'm just wondering about the reason to have it
> in
> > base.
> > Is it tied to TypeLits?
> >
> >
> > Cheers,
> > Pedro
> >
> > On Thu, Feb 7, 2013 at 2:21 PM, Gabor Greif <ggreif at gmail.com> wrote:
> >
> >> Oi José,
> >>
> >> this is a library-only issue, the branch is in libraries/base, thus
> >> somewhat tied to the 7.8 release.
> >>
> >> Cheers,
> >>
> >>     Gabor
> >>
> >> On 2/7/13, José Pedro Magalhães <jpm at cs.uu.nl> wrote:
> >> > On Wed, Feb 6, 2013 at 7:17 PM, Gabor Greif <ggreif at gmail.com> wrote:
> >> >
> >> >> On 2/6/13, Richard Eisenberg <eir at cis.upenn.edu> wrote:
> >> >> > The only thing that stops me from saying "push" is that I think
> >> >> > there
> >> >> > is
> >> >> a
> >> >> > better organization for all of this. The ideas we're discussing
> here
> >> >> (things
> >> >> > like the Void type) don't seem to belong in TypeLits -- it has
> >> >> > nothing
> >> >> to do
> >> >> > with literals. Time for a GHC.TypeReasoning module? Does someone
> >> >> > have
> >> a
> >> >> > better name?
> >> >>
> >> >> Sounds okay. We can wiggle around on the new branch 'till we feel
> >> >> comfortable, but I'd like to land this on master before the v7.8
> train
> >> >> leaves the station (i.e. the release branch is created).
> >> >>
> >> >
> >> > Can you perhaps summarise exactly what needs to be added to GHC for
> >> > this
> >> to
> >> > work?
> >> > It's not immediately clear to me why this is not just a library issue.
> >> >
> >> >
> >> > Thanks,
> >> > Pedro
> >> >
> >>
> >
>
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