"Simon Marlow"
On 09 December 2004 23:56, ross@soi.city.ac.uk wrote:
On Wed, Dec 08, 2004 at 10:42:26PM -0800, Isaac Jones wrote:
What about this interface for user-supplied command hooks. [...]
For each of the pre-functions, a Maybe PackageDescription is returned. If Nothing, then it gets the description from the file or the default description you passed in. If (Just p), then it uses the description returned by the pre-functions.
I'm not sure what's going on here. It seems only preConf needs to return anything, and that shouldn't be the whole PackageDescription (since you want part of that static), just the build information.
Each command needs access to the PackageDescription. The reason the hooks are like this is that we need to pass information between the commands via the file system. If the PreConf function were to return anything, it would be passed to configure, and all configure could do with it is write it to the configure file, which the future commands know how to read in, but that doesn't have the build information like the module list. So what the preConf step needs to do, is perhaps call autoconf on mySetup.description.in, and preBuild reads mySetup.description, likewise for preInstall. This is how we pass information from command to command. Isaac:
I don't particularly like the idea of: {{system "runhaskell" ["postinst.hs"]}} because it seems like a less elegant IO ExitCode. runhaskell doesn't exist, and it relies on more moving parts. Ross: Sure it exists -- I read about it in the spec.
Ross's solution lets you put the postinst code in the setup script itself, or optionally in an external script if you prefer. This seems more flexible to me.
The commands need a way to pass information between one-another. If we use 'system' to run external commands, then the only way to do that is to dump a file that cabal itself knows how to read back in, and cabal has to know where it is. If we rather use the preHooks, Angela can do whatever she wants to get the information between phases, so long as she returns a PackageDescription. If we use 'system' calls, then Cabal must specify the names of the scripts and the format and location of the files they output (or preHooks with an interface similar to mine to read them back in). If Cabal use the preHooks, then all we need to specify is the type of the functions. The preHooks let the user do the obvious thing, which is to read and write to a separate description file of their choosing, or to do something as strange as they like to get the package description. In any case, you can just say defaultUserFunctions{postInst=system "./postinst.hs">> readPackageDescription "thePlaceIKnowItWillEndUp"}. peace, isaac