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Simon Peyton Jones authored
Darn, but TcDeriv is complicated, when type families get in on the act! This patch makes GeneralisedNewtypeDeriving work properly for type families. I think. In order to do so, I found that GeneralisedNewtypeDeriving can work for recursive newtypes too -- and since families are conservatively marked recursive, that's a crucial part of the fix, and useful too. See Note [Recursive newtypes] in TcDeriv.
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