Strange No instance error with cabal install

Sometimes when one of our developers (using Arch-linux) tries to cabal install packages he gets a "no instance for" error. Code that compiles fine on my computer, and other computers I try it on. Even some packages on hackage (trying to install aeson-native for instance gives Data/Aeson/Types.hs:196:22: No instance for (NFData Object) arising from a use of `rnf' Possible fix: add an instance declaration for (NFData Object) In the expression: rnf o In an equation for `rnf': rnf (Object o) = rnf o In the instance declaration for `NFData Value') I tried removing the .ghc and .cabal folder, even reinstalled ghc-7.04 and cabal-install (most recent), but the problem persisted (might not have been a clean install though, I'm no Arch expert) I know this is kind of vauge, and not in she shape of filling a bug report, heck I can't even reproduce the error on my computer. But perhaps somebody else has run in to this strange behavior before? Best, Rune

I believe this is because of aeson depending on *any* version of
deepseq. This was very recently fixed in the development version:
https://github.com/mailrank/aeson/pull/25
2011/9/20 Rune Harder Bak
Sometimes when one of our developers (using Arch-linux) tries to cabal install packages he gets a "no instance for" error. Code that compiles fine on my computer, and other computers I try it on. Even some packages on hackage (trying to install aeson-native for instance gives Data/Aeson/Types.hs:196:22: No instance for (NFData Object) arising from a use of `rnf' Possible fix: add an instance declaration for (NFData Object) In the expression: rnf o In an equation for `rnf': rnf (Object o) = rnf o In the instance declaration for `NFData Value') I tried removing the .ghc and .cabal folder, even reinstalled ghc-7.04 and cabal-install (most recent), but the problem persisted (might not have been a clean install though, I'm no Arch expert) I know this is kind of vauge, and not in she shape of filling a bug report, heck I can't even reproduce the error on my computer. But perhaps somebody else has run in to this strange behavior before?
Best, Rune
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I see the aeson version with the stricter dependency on deepseq < 1.2 is now also released on hackage: http://hackage.haskell.org/package/aeson-0.3.2.12
participants (2)
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Roel van Dijk
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Rune Harder Bak