[Haskell-cafe] cabal doens't forget old dependencies

[Albert Y. C. Lai]

On 12-06-27 11:29 AM, Sjoerd Visscher wrote:
> I tried to install reactive-banana. This failed due to a dependency conflict, and then I noticed there was a newer version of reactive-banana. So I did cabal update, and tried to install again. But whatever I do, cabal keeps trying to install fclabels, but fclabels is no longer a dependency of reactive-banana-0.6.0.0! How can I let cabal forget this dependency?

In 
http://hackage.haskell.org/packages/archive/reactive-banana/0.6.0.0/reactive-banana.cabal 
:

if flag(UseExtensions)
         extensions:     TypeFamilies, GADTs, MultiParamTypeClasses,
                         BangPatterns, TupleSections,
                         EmptyDataDecls
         build-depends:  QuickCheck >= 1.2 && < 2.5,
                         fclabels == 1.1.*,
                         unordered-containers >= 0.2.1.0 && < 0.3,
                         hashable == 1.1.*
         CPP-options:    -DUseExtensions

Recall that the semantics of "if flag" is like Prolog not Pascal: if the 
packages under build-depends could be installed, then UseExtensions is 
set to true. Unless you manually override.