By the way, here's how I'm changing my code to work with the new and old arrow interface. I'd appreciate any suggested improvements. The old code (example): import Control.Arrow [...] instance Arrow (~>) => Arrow (Bijection (~>)) where Bi ab ba >>> Bi bc cb = Bi (ab >>> bc) (cb >>> ba) [...] The new code: #if __GLASGOW_HASKELL__ >= 609 import Control.Category import Prelude hiding ((.), id) #endif import Control.Arrow [...] #if __GLASGOW_HASKELL__ >= 609 instance Category (~>) => Category (Bijection (~>)) where id = Bi id id Bi bc cb . Bi ab ba = Bi (bc . ab) (ba . cb) #endif instance Arrow (~>) => Arrow (Bijection (~>)) where #if __GLASGOW_HASKELL__ < 609 Bi ab ba >>> Bi bc cb = Bi (ab >>> bc) (cb >>> ba) #endif [...] I'm testing for ghc version. Could I somehow test for the base-library version instead? - Conal On Tue, Jul 15, 2008 at 4:43 PM, Conal Elliott <conal@conal.net> wrote:
All code that defines Arrow instance breaks, because (>>>) is not a method of Arrow. I have a lot of such instances, so I'm now adding #if directives to test for ghc-6.9 or later. - Conal
On Mon, Jul 14, 2008 at 8:38 PM, Don Stewart <dons@galois.com> wrote:
conal:
I want to use ghc-6.9 for improved support of type families, but I see that the change to the Arrow interface breaks some of my libraries (since (>>>) is no longer a method of Arrow). Will this change really be in
(>>>) has been reexported from Control.Category through Arrow for a few months. Does that fix things, or is your code still broken?
-- Don