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Tao He authored
Summary: The element type of `List` maybe a type family instacen, rather than a trivial type. For example in Trac #14547, ``` {-# LANGUAGE TypeFamilies, OverloadedLists #-} class Foo f where type It f foo :: [It f] -> f data List a = Empty | a :! List a deriving Show instance Foo (List a) where type It (List a) = a foo [] = Empty foo (x : xs) = x :! foo xs ``` Here the element type of `[]` is `It (List a)`, we should also normalize it as `a`. Test Plan: make test TEST="T14547" Reviewers: bgamari Reviewed By: bgamari Subscribers: thomie, carter GHC Trac Issues: #14547 Differential Revision: https://phabricator.haskell.org/D4624
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