Documentation stale: implicit-parameter constraints seem to be allowed in instance declarations now.

http://www.haskell.org/ghc/docs/7.6.3/html/users_guide/other-type-extensions.html#implicit-parameters says:

You can't have an implicit parameter in the context of a class or instance declaration. For example, both these declarations are illegal:

  class (?x::Int) => C a where ...
  instance (?x::a) => Foo [a] where ...

However, ghc 7.6.3 seems to accept this now:

  {-# LANGUAGE ImplicitParams #-}

  class C a where
    toInt :: a -> Int

  instance (?imp :: Int) => C [a] where
    toInt _ = ?imp

  test :: Int 
  test = let ?imp = 5 in toInt "Hello, world"

test evaluates to 5.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Documentation
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