• mayac's avatar
    Fix #15828, from `More explicit foralls` · fe57a5ba
    mayac authored
    Fix a bug in commit 12eeb9 which permits the following:
    class C a where
      type T a b
    instance C (Maybe a) where
      type forall a b. T (Maybe a) b = b
    where instead, the user should write:
    instance C (Maybe a) where
      type forall b. T (Maybe a) b = b
    Update the users guide to discuss scoping of type variables in
    explicit foralls in type family instances.
    Test Plan: validate
    Reviewers: bgamari, goldfire, monoidal
    Reviewed By: goldfire
    Subscribers: monoidal, rwbarton, carter
    GHC Trac Issues: #15828
    Differential Revision: https://phabricator.haskell.org/D5283
glasgow_exts.rst 588 KB