Changes to the type checker with respect to UndecidableInstances

[Mitsutoshi Aoe]

Hi,

I found a difference between GHC 7.6.3 and 7.8.3 with respect to UndecidableInstances.

https://gist.github.com/maoe/57a4346eb36aee159916 <https://gist.github.com/maoe/57a4346eb36aee159916>

7.6.3 requires UndecidableInstances to compile this snippet whereas 7.8.3 doesn't. What has changed in the type checker?

Mitsutoshi

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