On 7/27/05, Duncan Coutts
On Wed, 2005-07-27 at 16:10 -0500, Brian Smith wrote:
In short, the cabal package description is not the only information you need to fully describe how to successfully build an application.
If we hope to have cabal packages properly supported by packaging systems (which I believe we do) then this sort of information is essential. And I think that it is important that it is discoverable automatically. If most packages in the hackage collection require manual fiddling and fixing then it will not be practical to mirror the hackage collection in normal distro packaging systems.
I think it is essential to be able to tell which build infrastructure is being used, and which hooks need to be executed, without looking at Setup.lhs. In fact, I think that the relationship between the Setup.hs and Package.cabal file is backwards. Imagine that there was no "Setup.hs," and that every Haskell implementation came with an executable that could process Cabal files. Now, let's say a Cabal package descriptions had these entries: Build-Infrastructure: Simple Hooks: None This would mean that the Simple build infrastructure is being used, and that there are no hooks; it is equivalent to Distribution.Simple.defaultMain. Note that the default value of Hooks could be "None" and the default Build-Infrastructure could be "Simple." If a package description had these entries: Build-Infrastructure: Simple Hooks: Setup (preBuild, postBuild, postClean) it has the three hooks mentioned, which are exported from the package's Setup module. Each hook is just a function with the same type it has from Distribution.Simple.UserHooks. Each implementations's setup tool would determine how to call these hooks. Now, if a package description had this entry: Build-Infrastructure: Make Then, tools that don't have Make (e.g. VHS.NET) could gracefully say "Make is not a supported build infrastructure" or "Cannot build this package because make is not installed." Also, imagine being able to do this for a Cabal package that has: Build-Depends: HUnit, HaXml $ ghci --cabal My.Module Loading package base-1.0 ... linking ... done. Loading package haskell98-1.0 ... linking ... done. Loading package HaXml-1.13 ... linking ... done. Loading package HUnit-1.1 ... linking ... done. My.Module> instead of: $ ghci -package HUnit -package HaXml - Brian