Re: [Haskell-cafe] Building lambdabot

On Thu, Jan 20, 2011 at 12:45 PM, Max Bolingbroke wrote:

On 20 January 2011 17:30, Gwern Branwen wrote:

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* You need to loosen the base upper bound to < 4.4 * If using base >= 4, you need to depend on the syb package as well (current version 0.3)

Would this break GHC 6.12 builds?

Thats why I suggested the flag stanza. Cabal has a weird kind of flag semantics where it will try every possible combination of flags until it finds one that builds. The solution I suggested uses this behaviour to either depend on base >= 4 && < 4.4 WITH syb, OR base < 4 WITHOUT syb. Because of the default flag setting of True, the first possibility will be tried first, but it if fails Cabal will just fall back on base < 4.

In short, it should work perfectly for either GHC 7 or 6.12 clients (modulo syntax issues - I haven't actually tried the syntax I sent you).

No, there's another issue. I've recorded this version; hunk ./show/show.cabal 25 +Flag base4 + Description: Build with base-4 + Default: False + hunk ./show/show.cabal 32 - build-depends: base<4, random, QuickCheck>=2.4, smallcheck>=0.4 + build-depends: random, QuickCheck>=2.4, smallcheck>=0.4 + if flag(base4) + build-depends: base>=4 && <4.4, syb >= 0.3 && < 0.4 + else + build-depends: base<4 Notice the flag defaults to False, not True. When I tried it with True, I got: $ cabal install Resolving dependencies... cabal: dependencies conflict: base-3.0.3.2 requires syb ==0.1.0.2 however syb-0.1.0.2 was excluded because syb-0.3 was selected instead syb-0.1.0.2 was excluded because show-0.4.1 requires syb ==0.3.* -- gwern http://www.gwern.net