Hi Stefan
Thanks for a very enlightening reply.
In GHC 6.7.20070712 and Yhc, this is perfectly safe.
In GRIN based systems like Jhc, this is *not* safe, since after
evaluation comparisons are done using the full tag.
It's now occurred to me that at a cost of some noise, I could have
done things
a little differently
On 14 Jul 2007, at 20:37, Stefan O'Rear wrote:
On Sat, Jul 14, 2007 at 12:06:30PM +0100, Conor McBride wrote:
A peculiar query for folks who know more about the internals of
Haskell
compilers than I do. I attach the full code with all the bits and
pieces,
but let me pull out the essentials in order to state the problem.
newtype Id x = Id x -- element
newtype K1 a x = K1 a -- constant
> newtype Up1 f p q x = U1 (f (p x) (q x))
> type Sum1 = Up1 Either
> type Prod1 = Up1 (,)
newtype Fst x y = Fst x
newtype Snd x y = Snd y
newtype K2 a x y = K2 a
> newtype Up2 f p q x y = U2 (f (p x y) (q x y))
> type Sum2 = Up2 Either
> type Prod2 = Up2 (,)
class (Bifunctor b, Functor f) => Diag b f | b -> f where
diag :: b x x -> f x
gaid :: f x -> b x x
and then all of my coercions would (recursively) have been between
newtype-isotopes.
Would that have more universal traction? I realise, of course that it's
all voodoo, and I shouldn't trust a thing.
Cheers
Conor
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
