[Haskell-cafe] [weird stuff] The Dodgy Diagonal
Conor McBride
ctm at Cs.Nott.AC.UK
Sat Jul 14 16:09:48 EDT 2007
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
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