+1 on all of the above, I generally find my proxy code is nicest when i'm polymoprophic over the prox :) On Wed, Aug 14, 2019 at 12:45 PM Eric Mertens wrote:

While we’re fixing that, let’s also fix sameSymbol.

...

On Aug 13, 2019, at 4:32 PM, Andrew Lelechenko < andrew.lelechenko@gmail.com> wrote:

Hi all,

Currently base:GHC.TypeNats.sameNat is implemented as follows:

sameNat :: (KnownNat a, KnownNat b) => Proxy a -> Proxy b -> Maybe (a :~: b) sameNat x y | natVal x == natVal y = Just (unsafeCoerce Refl) | otherwise = Nothing

There are applications, when more flexibility is desirable. I propose to change sameNat's type to

sameNat :: (KnownNat a, KnownNat b) => proxy1 a -> proxy2 b -> Maybe (a :~: b)

It does not require any changes in the implementation, because natVal is already "proxy-polymorphic":

natVal :: forall n proxy. KnownNat n => proxy n -> Natural

Best regards, Andrew _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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