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Diffstat (limited to 'docs/users_guide')
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 53 |
1 files changed, 0 insertions, 53 deletions
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index 03ca184531..27efd9f899 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -123,7 +123,6 @@ The following flags are simple ways to select standard "packages" of warnings: * :ghc-flag:`-Wmissing-monadfail-instances` * :ghc-flag:`-Wsemigroup` * :ghc-flag:`-Wnoncanonical-monoid-instances` - * :ghc-flag:`-Wimplicit-kind-vars` * :ghc-flag:`-Wstar-is-type` .. ghc-flag:: -Wno-compat @@ -776,58 +775,6 @@ of ``-W(no-)*``. This warning is off by default. -.. ghc-flag:: -Wimplicit-kind-vars - :shortdesc: warn when kind variables are brought into scope implicitly despite - the "forall-or-nothing" rule - :type: dynamic - :reverse: -Wno-implicit-kind-vars - :category: - - :since: 8.6 - - `GHC proposal #24 - <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0024-no-kind-vars.rst>`__ - prescribes to treat kind variables and type variables identically in - ``forall``, removing the legacy distinction between them. - - Consider the following examples: :: - - f :: Proxy a -> Proxy b -> () - g :: forall a b. Proxy a -> Proxy b -> () - - ``f`` does not use an explicit ``forall``, so type variables ``a`` and ``b`` - are brought into scope implicitly. ``g`` quantifies both ``a`` and ``b`` - explicitly. Both ``f`` and ``g`` work today and will continue to work in the - future because they adhere to the "forall-or-nothing" rule: either all type - variables in a function definition are introduced explicitly or implicitly, - there is no middle ground. - - A violation of the "forall-or-nothing" rule looks like this: :: - - m :: forall a. Proxy a -> Proxy b -> () - - ``m`` does not introduce one of the variables, ``b``, and thus is rejected. - - However, consider the following example: :: - - n :: forall a. Proxy (a :: k) -> () - - While ``n`` uses ``k`` without introducing it and thus violates the rule, it - is currently accepted. This is because ``k`` in ``n`` is considered a kind - variable, as it occurs in a kind signature. In reality, the line between - type variables and kind variables is blurry, as the following example - demonstrates: :: - - kindOf :: forall a. Proxy (a :: k) -> Proxy k - - In ``kindOf``, the ``k`` variable is used both in a kind position and a type - position. Currently, ``kindOf`` happens to be accepted as well. - - In a future release of GHC, both ``n`` and ``kindOf`` will be rejected per - the "forall-or-nothing" rule. This warning, being part of the - :ghc-flag:`-Wcompat` option group, allows to detect this before the actual - breaking change takes place. - .. ghc-flag:: -Wincomplete-patterns :shortdesc: warn when a pattern match could fail :type: dynamic |