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Tom Murphy authored
Expressions like the following will now typecheck: ``` data A x = A deriving Show class ToA a x where toA :: a -> A x instance ToA Integer x where toA _ = A main = print (toA 5 :: A Bool) ``` The new defaulting rules are Find all the unsolved constraints. Then: * Find those that have exactly one free type variable, and partition that subset into groups that share a common type variable `a`. * Now default `a` (to one of the types in the default list) if at least one of the classes `Ci` is an interactive class Reviewers: goldfire, bgamari, austin, mpickering, simonpj Reviewed By: bgamari, simonpj Subscribers: mpickering, simonpj, goldfire, thomie Differential Revision: https://phabricator.haskell.org/D2822
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