On Thu, Jan 31, 2013 at 12:28 PM, Henning Thielemann < lemming@henning-thielemann.de> wrote:
On Thu, 31 Jan 2013, Thomas Schilling wrote:
I don't think this would work. If "network" still contains a module
Network.URI and a package adds a dependency on "network-uri" which also exports a module Network.URI, then you would have to specify the package name in your import, i.e.:
import "network-uri" Network.URI
Then, once Network.URI is removed from "network", users have to edit their sources again to remove the explicit package import. I think the only reasonable way to handle things is to use flags in a .cabal file, i.e., the same way we had to deal with base-3 => base-4 transition (which was very annoying).
An alternative would be to split the "network" package into "network-uri" and "network-socket". Users of network-uri would have to switch to network-socket as well. However, the types of "network" and "network-socket" would be incompatible unless the "network-socket" package re-exports the modules from "network" or vice versa.
E.g. could we put this into the "network" package:
{-# LANGUAGE PackageImports #-} module Network.Socket ( module S ) where
import qualified "network-socket" Network.Socket as S
?
Interestingly, the GHC documentation uses Network.Socket for explaining the PackageImports extension.
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Recently, we have a similar situation with http-conduit. Based on that, I'd recommend going for a conditional export situation. * Release a new version of network (1.5) that does not include the Network.URI module. * Create a network-uri package that uses conditionals in the cabal file. * If it's compiled against network version 1.4 or earlier, it doesn't provide any modules. * If it's compiled against network 1.5 or later, it provides the Network.URI module. This way, there's only ever one package which is providing Network.URI. Note: I think there might be a requirement that a library section always have at least one exported module. If so, I suppose network-uri should always export some extra package as well, perhaps Network.URI.Temp which contains everything in Network.URI. Michael