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Simon Peyton Jones authored
This fixes most of Trac #3990. Consider data family D a data instance D Double = CD Int Int data T = T {-# UNPACK #-} !(D Double) Then we want the (D Double unpacked). To do this we need to construct a suitable coercion, and it's much safer to record that coercion in the interface file, lest the in-scope instances differ somehow. That in turn means elaborating the HsBang type to include a coercion. To do that I moved HsBang from BasicTypes to DataCon, which caused quite a few minor knock-on changes. Interface-file format has changed! Still to do: need to do knot-tying to allow instances to take effect within the same module.
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