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| author | Torsten Schmits <git@tryp.io> | 2022-07-18 19:44:50 +0200 |
|---|---|---|
| committer | Torsten Schmits <git@tryp.io> | 2022-07-18 19:44:50 +0200 |
| commit | a40e63fee44891f4418592f7994243b72fd90a8c (patch) | |
| tree | 80a20129b233fb890d64a7342a0f9d23960dbfbb | |
| parent | 92e141666d5c206d0504aa3cb234d7f2f4e5e787 (diff) | |
| download | haskell-a40e63fee44891f4418592f7994243b72fd90a8c.tar.gz | |
add -Wpattern-signature-binds to user guide
| -rw-r--r-- | docs/users_guide/exts/scoped_type_variables.rst | 3 | ||||
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 14 |
2 files changed, 17 insertions, 0 deletions
diff --git a/docs/users_guide/exts/scoped_type_variables.rst b/docs/users_guide/exts/scoped_type_variables.rst index fa117fc032..e10454e8db 100644 --- a/docs/users_guide/exts/scoped_type_variables.rst +++ b/docs/users_guide/exts/scoped_type_variables.rst @@ -227,6 +227,9 @@ case, *the signature brings that type variable into scope*. For example: :: The pattern type signature makes the type variable available on the right-hand side of the equation. +GHC will print a warning about variables brought into scope by signatures +in this fashion if the flag :ghc-flag:`-Wpattern-signature-binds` is set. + Bringing type variables into scope is particularly important for existential data constructors. For example: :: diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index 977bb69941..80f91f4f5f 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -129,6 +129,7 @@ The following flags are simple ways to select standard "packages" of warnings: * :ghc-flag:`-Wimplicit-lift` * :ghc-flag:`-Wmissing-kind-signatures` * :ghc-flag:`-Wunticked-promoted-constructors` + * :ghc-flag:`-pattern-signature-binds` .. ghc-flag:: -Weverything :shortdesc: enable all warnings supported by GHC @@ -2355,6 +2356,19 @@ of ``-W(no-)*``. triggered whenever this happens, and can be addressed by enabling the extension. +.. ghc-flag:: -Wpattern-signature-binds + :shortdesc: warn when a pattern signature binds a type variable + :type: dynamic + :reverse: -Wno-pattern-signature-binds + + :since: 9.6 + + :extension:`ScopedTypeVariables` allows patterns to be annotated with type signatures. + If a signature mentions a type variable that hasn't been explicitly quantified in a + ``forall``, GHC will implicitly bind it. + This warning reports such an implicitly bound variable. + + 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 sanity, not yours.) |