Error when trying to derive Arrow (Kleisli m)

[koflerdavid]

Hello,

today I played around with Djinn a bit, and noticed what I am pretty sure is a bug:
I added a definition for an Arrow typeclass, and the Kleisli wrapper for a Monad.
Then, I tried to derive an instance Arrow (Kleisli m).

Input:

Djinn> class Arrow arr where id :: arr a a; (.) :: arr b c -> arr a b -> arr a c; toArr :: (b -> c) -> arr b c; first :: arr b c -> arr (b, d) (c, d)
Djinn> data Kleisli m a b = MkKleisli (a -> m b)
Djinn> ?instance Arrow (Kleisli m)

Expected result: an instance Arrow (Kleisli m) or a message that this is not possible.
Actual result: an error:

Djinn> ?instance Arrow (Kleisli m)
instance Arrow (Kleisli m) where
djinn: IntMap.!: key 3 is not an element of the map
CallStack (from HasCallStack):
error, called at libraries/containers/Data/IntMap/Internal.hs:569:17 in containers-0.5.10.2:Data.IntMap.Internal

I'll try to shrink the example, but so far this is all I have.

Best regards,
David Kofler

[augustss]

Djinn cannot handle higher kinder type variables very well. But it doesn’t tell you so.

…

On Wed, Jun 6, 2018 at 09:18 David Kofler ***@***.***> wrote: Hello, today I played around with Djinn a bit, and noticed what I am pretty sure is a bug: I added a definition for an Arrow typeclass, and the Kleisli wrapper for a Monad. Then, I tried to derive an instance Arrow (Kleisli m). Input: Djinn> class Arrow arr where id :: arr a a; (.) :: arr b c -> arr a b -> arr a c; toArr :: (b -> c) -> arr b c; first :: arr b c -> arr (b, d) (c, d) Djinn> data Kleisli m a b = MkKleisli (a -> m b) Djinn> ?instance Arrow (Kleisli m) Expected result: an instance Arrow (Kleisli m) or a message that this is not possible. Actual result: an error: Djinn> ?instance Arrow (Kleisli m) instance Arrow (Kleisli m) where djinn: IntMap.!: key 3 is not an element of the map CallStack (from HasCallStack): error, called at libraries/containers/Data/IntMap/Internal.hs:569:17 in containers-0.5.10.2:Data.IntMap.Internal I'll try to shrink the example, but so far this is all I have. Best regards, David Kofler — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#6>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFAInrJtfYG-yALZ66tpA4luCZ7BN3Q5ks5t6ADJgaJpZM4Uc9VO> .