Thanks, I missed that the flags are set dynamically if a dependency
cannot be satisfied.
Am 17.03.2010 13:23 schrieb Daniel Fischer:
Am Mittwoch 17 März 2010 12:11:53 schrieb Matthias Reisner:
Hi,
for a package I need to ensure the user uses a certain package
configuration. So how would I rewrite the following pseudo-cabal
description?
Build-Depends: packageA < X, packageB < Y
or
packageA >= X && < X', packageB >= Y && < Y'
or
packageA >= X', packageB >= Y'
Build-Depends: ... common dependencies ...
where neither A nor B is the base package. Maybe I have to use if/else
blocks, but I don't know what conditions to use then.
Read http://www.haskell.org/ghc/docs/latest/html/Cabal/authors.html for a
general description of what you can do, I'd try something like in
http://hackage.haskell.org/packages/archive/cabal-install/0.8.0/cabal-
install.cabal
flag oldAB
description: ancient packages A and B
default: False
flag newAB
description: shiny new A and B
Library blubb
build-depends:
common,
libraries
if flag(newAB)
build-depends: packageA >= X', packageB >= Y'
else if flag(oldAB)
build-depends: packageA < X, packageB < Y
else
build-depends: packageA >= X && < X', packageB >= Y && < Y'
If I remember correctly, that tries first to build against the new A and B,
that failing, it sets flag newAB to false and tries again, first with the
not-so-ancient A and B, hopefully (but I'm not sure about the order in
which flags are toggled if the defaults don't give a successful install
plan).
Regards,
Matthias
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