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Diffstat (limited to 'docs/users_guide/using-warnings.rst')
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index 07ddbb12d5..fb9c913500 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -224,6 +224,28 @@ of ``-W(no-)*``. This option is off by default. +.. ghc-flag:: -Wnoncanonical-monadfail-instances + + Warn if noncanonical ``Monad`` or ``MonadFail`` instances + declarations are detected. + + When this warning is enabled, the following conditions are verified: + + In ``Monad`` instances declarations warn if any of the following + conditions does not hold: + + * If ``fail`` is defined it must be canonical + (i.e. ``fail = Control.Monad.Fail.fail``). + + Moreover, in ``MonadFail`` instance declarations: + + * Warn if ``fail`` is defined backwards + (i.e. ``fail = Control.Monad.fail``). + + See also :ghc-flag:`-Wmissing-monadfail-instance`. + + This option is off by default. + .. ghc-flag:: -Wnoncanonical-monoid-instances Warn if noncanonical ``Semigroup`` or ``Monoid`` instances @@ -253,6 +275,8 @@ of ``-W(no-)*``. Warn when a failable pattern is used in a do-block that does not have a ``MonadFail`` instance. + See also :ghc-flag:`-Wnoncanonical-monadfail-instances`. + Being part of the :ghc-flag:`-Wcompat` option group, this warning is off by default, but will be switched on in a future GHC release, as part of the `MonadFail Proposal (MFP) |