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Ningning Xie authored
Summary: The patch is an attempt on #15192. It defines a new coercion rule ``` | GRefl Role Type MCoercion ``` which correspondes to the typing rule ``` t1 : k1 ------------------------------------ GRefl r t1 MRefl: t1 ~r t1 t1 : k1 co :: k1 ~ k2 ------------------------------------ GRefl r t1 (MCo co) : t1 ~r t1 |> co ``` MCoercion wraps a coercion, which might be reflexive (MRefl) or not (MCo co). To know more about MCoercion see #14975. We keep Refl ty as a special case for nominal reflexive coercions, naemly, Refl ty :: ty ~n ty. This commit is meant to be a general performance improvement, but there are a few regressions. See #15192, comment:13 for more information. Test Plan: ./validate Reviewers: bgamari, goldfire, simonpj Subscribers: rwbarton, thomie, carter GHC Trac Issues: #15192 Differential Revision: https://phabricator.haskell.org/D4747
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