Add bivoid (#28)

* Add bivoid

* Add bivoid to Changelog

---------

Co-authored-by: Michael Bock <michael.bock@visonum.de>

Author: m-bock

CHANGELOG.md

@@ -7,6 +7,7 @@ Notable changes to this project are documented in this file. The format is based
 Breaking changes:
 
 New features:
+  - Added `bivoid` 
 
 Bugfixes:
 

src/Data/Bifunctor.purs

@@ -4,6 +4,8 @@ import Control.Category (identity)
 import Data.Const (Const(..))
 import Data.Either (Either(..))
 import Data.Tuple (Tuple(..))
+import Data.Unit (Unit, unit)
+import Data.Function (const)
 
 -- | A `Bifunctor` is a `Functor` from the pair category `(Type, Type)` to `Type`.
 -- |
@@ -29,6 +31,10 @@ lmap f = bimap f identity
 rmap :: forall f a b c. Bifunctor f => (b -> c) -> f a b -> f a c
 rmap = bimap identity
 
+-- | The bivoid function is used to ignore the types wrapped by a Bifunctor.
+bivoid :: forall f a b. Bifunctor f => f a b -> f Unit Unit
+bivoid = bimap (const unit) (const unit)
+
 instance bifunctorEither :: Bifunctor Either where
   bimap f _ (Left l) = Left (f l)
   bimap _ g (Right r) = Right (g r)