Re: Proposal: Lifting to TExpQ

Cool! Yeah, the name bikeshedding on typedLift vs liftT is that "lift" is already too transformer-ey for my taste, and liftT makes it even moreso. Also, I realized I mistyped the type of 'lift', it should be 'Lift t => t -> Q Exp'. -Michael On Sun, Jan 14, 2018 at 12:05 PM, Dan Burton wrote:

+1 to Michael's suggestion; that's basically the same thing I would have suggested, modulo bikeshedding.

On Jan 13, 2018 15:03, "Michael Sloan" wrote:

Hmm, I'm not sure about changing the Lift class, there are good reasons to leave it the same and good reasons to change as well. There is a lot of precedent for providing safe functions which use unsafe functions (e.g. unsafeDupablePerformIO in bytestring / text). Also, not much of the TH API uses TExp, just typed splices. On the other hand, it does make the method's type stronger and directly suggest more properties. It may encourage people to use typed splices to define manual instances, which I think is good.

I propose a somewhat less breaking change, defining the following:

class Lift t where typedLift :: t -> Q (TExp t)

lift :: Lift t => t -> Q t lift = fmap unType . typedLift

The advantage of this is that a lot more code depends on usage of 'lift' than defining instances of 'Lift'. A lot of the code that defines instances of 'Lift' does it via the 'th-lift' package. I believe that only a handful of packages would need to be updated as a result of this change, vs the dozens that would need to be updated by changing the type of 'lift'.

Even after this change, I think that since 'TExp' is only useful with typed splices, the 'lift' form would still find much more usage as the more convenient function.

-Michael _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries