    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.Build.Macros
    -- Copyright   :  Simon Marlow 2008
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- Generate cabal_macros.h - CPP macros for package version testing
    --
    -- When using CPP you get
    --
    -- > VERSION_<package>
    -- > MIN_VERSION_<package>(A,B,C)
    --
    -- for each /package/ in @build-depends@, which is true if the version of
    -- /package/ in use is @>= A.B.C@, using the normal ordering on version
    -- numbers.
    --
    module Distribution.Simple.Build.Macros (
        generate
      ) where

    import Distribution.Package
             ( PackageIdentifier(PackageIdentifier) )
    import Distribution.Version
             ( Version(versionBranch) )
    import Distribution.PackageDescription
             ( PackageDescription )
    import Distribution.Simple.LocalBuildInfo
            ( LocalBuildInfo, externalPackageDeps )
    import Distribution.Text
             ( display )

    -- ------------------------------------------------------------
    -- * Generate cabal_macros.h
    -- ------------------------------------------------------------

    generate :: PackageDescription -> LocalBuildInfo -> String
    generate _pkg_descr lbi = concat $
      "/* DO NOT EDIT: This file is automatically generated by Cabal */\n\n" :
      [ concat
        ["/* package ",display pkgid," */\n"
        ,"#define VERSION_",pkgname," ",show (display version),"\n"
        ,"#define MIN_VERSION_",pkgname,"(major1,major2,minor) (\\\n"
        ,"  (major1) <  ",major1," || \\\n"
        ,"  (major1) == ",major1," && (major2) <  ",major2," || \\\n"
        ,"  (major1) == ",major1," && (major2) == ",major2," && (minor) <= ",minor,")"
        ,"\n\n"
        ]
      | (_, pkgid@(PackageIdentifier name version)) <- externalPackageDeps lbi
      , let (major1:major2:minor:_) = map show (versionBranch version ++ repeat 0)
            pkgname = map fixchar (display name)
      ]
      where fixchar '-' = '_'
            fixchar c   = c