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| author | Herbert Valerio Riedel <hvr@gnu.org> | 2019-12-08 11:47:58 +0100 |
|---|---|---|
| committer | Herbert Valerio Riedel <hvr@gnu.org> | 2019-12-08 12:08:16 +0100 |
| commit | ee05ff1ecde866e31f72e3fa4f773dca98944dc3 (patch) | |
| tree | fbec72f1cb8707903b872ab6bd7a0f81c4850839 | |
| parent | e6ca100973c496cd98da3385594fa9a81320f7cb (diff) | |
Document error-prone conditional definition of instances
This can easily trip up people if one isn't aware of it. Usually it's
better to avoid this kind of conditionality especially for typeclasses
for which there's an compat-package as conditional instances like
these tend to fragment the ecosystem into those packages that go the
extra mile to provide backward compat via those compat-packages and
those that fail to do so.
| -rw-r--r-- | haddock-library/src/Documentation/Haddock/Types.hs | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/haddock-library/src/Documentation/Haddock/Types.hs b/haddock-library/src/Documentation/Haddock/Types.hs index ba2f873c..4cf61fee 100644 --- a/haddock-library/src/Documentation/Haddock/Types.hs +++ b/haddock-library/src/Documentation/Haddock/Types.hs @@ -44,14 +44,17 @@ data MetaDoc mod id = } deriving (Eq, Show, Functor, Foldable, Traversable) #if MIN_VERSION_base(4,8,0) +-- | __NOTE__: Only defined for @base >= 4.8.0@ instance Bifunctor MetaDoc where bimap f g (MetaDoc m d) = MetaDoc m (bimap f g d) #endif #if MIN_VERSION_base(4,10,0) +-- | __NOTE__: Only defined for @base >= 4.10.0@ instance Bifoldable MetaDoc where bifoldr f g z d = bifoldr f g z (_doc d) +-- | __NOTE__: Only defined for @base >= 4.10.0@ instance Bitraversable MetaDoc where bitraverse f g (MetaDoc m d) = MetaDoc m <$> bitraverse f g d #endif @@ -131,6 +134,7 @@ data DocH mod id deriving (Eq, Show, Functor, Foldable, Traversable) #if MIN_VERSION_base(4,8,0) +-- | __NOTE__: Only defined for @base >= 4.8.0@ instance Bifunctor DocH where bimap _ _ DocEmpty = DocEmpty bimap f g (DocAppend docA docB) = DocAppend (bimap f g docA) (bimap f g docB) @@ -159,6 +163,7 @@ instance Bifunctor DocH where #endif #if MIN_VERSION_base(4,10,0) +-- | __NOTE__: Only defined for @base >= 4.10.0@ instance Bifoldable DocH where bifoldr f g z (DocAppend docA docB) = bifoldr f g (bifoldr f g z docA) docB bifoldr f g z (DocParagraph doc) = bifoldr f g z doc @@ -176,6 +181,7 @@ instance Bifoldable DocH where bifoldr f g z (DocTable (Table header body)) = foldr (\r acc -> foldr (flip (bifoldr f g)) acc r) (foldr (\r acc -> foldr (flip (bifoldr f g)) acc r) z body) header bifoldr _ _ z _ = z +-- | __NOTE__: Only defined for @base >= 4.10.0@ instance Bitraversable DocH where bitraverse _ _ DocEmpty = pure DocEmpty bitraverse f g (DocAppend docA docB) = DocAppend <$> bitraverse f g docA <*> bitraverse f g docB |