diff options
Diffstat (limited to 'docs/users_guide/using-warnings.rst')
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index f603a4cf28..f0c4ac4fd5 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -1503,7 +1503,7 @@ of ``-W(no-)*``. do { mapM_ popInt xs ; return 10 } .. ghc-flag:: -Wunused-type-patterns - :shortdesc: warn about unused type variables which arise from patterns + :shortdesc: warn about unused type variables which arise from patterns in in type family and data family instances :type: dynamic :reverse: -Wno-unused-type-patterns @@ -1513,22 +1513,30 @@ of ``-W(no-)*``. single: unused type patterns, warning single: type patterns, unused - Report all unused type variables which arise from patterns in type family - and data family instances. For instance: :: + Report all unused implicitly bound type variables which arise from + patterns in type family and data family instances. For instance: :: type instance F x y = [] - would report ``x`` and ``y`` as unused. The warning is suppressed if the - type variable name begins with an underscore, like so: :: + would report ``x`` and ``y`` as unused on the right hand side. The warning + is suppressed if the type variable name begins with an underscore, like + so: :: type instance F _x _y = [] + When :extension:`ExplicitForAll` is enabled, explicitly quantified type + variables may also be identified as unused. For instance: :: + + type instance forall x y. F x y = [] + + would still report ``x`` and ``y`` as unused on the right hand side + Unlike :ghc-flag:`-Wunused-matches`, :ghc-flag:`-Wunused-type-patterns` is not implied by :ghc-flag:`-Wall`. The rationale for this decision is that unlike term-level pattern names, type names are often chosen expressly for documentation purposes, so using underscores in type names can make the documentation harder to read. - + .. ghc-flag:: -Wunused-foralls :shortdesc: warn about type variables in user-written ``forall``\\s that are unused |