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Problem: In 2463df2f, the Solo data constructor was renamed to MkSolo, and Solo was turned into a pattern synonym for backwards compatibility. Since pattern synonyms can not be promoted, the old code that pretty-printed promoted single-element tuples started producing ill-typed code: t :: Proxy ('Solo Int) This fails with "Pattern synonym ‘Solo’ used as a type" The solution is to track the distinction between type constructors and data constructors more carefully when printing single-element tuples.
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