On Mon, 2009-11-16 at 12:28 +0100, Mikhail Glushenkov wrote:

Hi,

On Mon, Nov 16, 2009 at 1:47 AM, Duncan Coutts wrote:

...

These packages all use "build-depends: base >= 3 && < 5" (except for ghc-core which cheekily uses "build-depends: base < 10" --- a practise we will ban if it becomes any more popular).

I have one question. It looks like the recommended way to solve the problem is to use something like:

Flag separateSYB Description: Data.Generics available in separate package.

[...] if flag(separateSYB) build-Depends: base >= 3 && < 4 else build-Depends: base >= 4 && < 5, syb

When the user types 'cabal install pointful' (without providing -fseparateSYB), which version of base will be the executable built against?

It prefers the default value of the flag. If that's impossible then it tries with the non-default flag value. When you do not specify a default flag value, the default is True. So as you've written it, in the absence of any constraints it'll pick the separateSYB=True configuration, which as you've written it, will *not* use the separate syb package. I think you intended to write it the other way around. Duncan