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Diffstat (limited to 'docs/users_guide/using-warnings.rst')
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index 922a9638c0..9d0ab1f667 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -2415,6 +2415,28 @@ of ``-W(no-)*``. In other words the type-class role cannot be accidentally left representational or phantom, which could affected the code correctness. +.. ghc-flag:: -Wpattern-signature-binds + :shortdesc: warn when pattern signature binds new type variable + :type: dynamic + + :since: 9.8.1 + + Added in accordance with `GHC Proposal #448 + <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0448-type-variable-scoping.rst>`__. + + Type variable bindings in pattern signatures violate the Lexical Scoping Principle: depending + on the context, type variables in the pattern signatures can be either occurrences or bindings. + + For example: :: + + f (x :: a) = ... -- binding of ‘a’ + + g :: forall a . ... + g (x :: a) = ... -- occurrence of ‘a’ + + When :ghc-flag:`-Wpattern-signature-binds` is enabled, GHC warns agains type variable bindings + in pattern signatures. + If you're feeling really paranoid, the :ghc-flag:`-dcore-lint` option is a good choice. It turns on heavyweight intra-pass sanity-checking within GHC. (It checks GHC's |