diff --git a/src/Data/Inject.purs b/src/Data/Inject.purs
deleted file mode 100644
index fb044c1..0000000
--- a/src/Data/Inject.purs
+++ /dev/null
@@ -1,41 +0,0 @@
--- | This module defines a type class `Inject` which is useful
--- | when working with coproducts of functors.
-
-module Data.Inject
-  ( class Inject
-  , inj, prj
-  ) where
-
-import Prelude (const, (<<<), id)
-
-import Data.Either (Either(..))
-import Data.Functor.Coproduct (Coproduct(..), coproduct)
-import Data.Maybe (Maybe(..))
-
--- | The `Inject` class asserts a coproduct relationship between two functors.
--- |
--- | Specifically, an instance `Inject f g` indicates that `g` is isomorphic to
--- | a coproduct of `f` and some third functor.
--- |
--- | Laws:
--- |
--- | - `prj g = Just f` if and only if `inj f = g`
-class Inject f g where
-  inj :: forall a. f a -> g a
-  prj :: forall a. g a -> Maybe (f a)
-
--- | Any functor is isomorphic to the coproduct of itself with the
--- | constantly-`Void` functor.
-instance injectReflexive :: Inject f f where
-  inj = id
-  prj = Just
-
--- | Left injection
-instance injectLeft :: Inject f (Coproduct f g) where
-  inj = Coproduct <<< Left
-  prj = coproduct Just (const Nothing)
-
--- | Right injection
-instance injectRight :: (Inject f g) => Inject f (Coproduct h g) where
-  inj = Coproduct <<< Right <<< inj
-  prj = coproduct (const Nothing) prj
diff --git a/src/Data/Inject/Coproduct.purs b/src/Data/Inject/Coproduct.purs
new file mode 100644
index 0000000..0527bb6
--- /dev/null
+++ b/src/Data/Inject/Coproduct.purs
@@ -0,0 +1,23 @@
+module Data.Inject.Either where
+
+import Prelude
+
+import Data.Either (Either(..))
+import Data.Functor.Coproduct (Coproduct(..), coproduct)
+import Data.Maybe (Maybe(..))
+
+class Inject f g where
+  inj :: forall a. f a -> g a
+  prj :: forall a. g a -> Maybe (f a)
+
+instance injectLeft :: Inject f g => Inject f (Coproduct g h) where
+  inj = Coproduct <<< Left <<< inj
+  prj = coproduct prj (const Nothing)
+
+else instance injectRight :: Inject f g => Inject f (Coproduct h g) where
+  inj = Coproduct <<< Right <<< inj
+  prj = coproduct (const Nothing) prj
+
+else instance injectReflexive :: Inject f f where
+  inj = id
+  prj = Just
diff --git a/src/Data/Inject/Either.purs b/src/Data/Inject/Either.purs
new file mode 100644
index 0000000..364e6a8
--- /dev/null
+++ b/src/Data/Inject/Either.purs
@@ -0,0 +1,22 @@
+module Data.Inject.Either where
+
+import Prelude
+
+import Data.Either (Either(..), either)
+import Data.Maybe (Maybe(..))
+
+class Inject a b where
+  inj :: a -> b
+  prj :: b -> Maybe a
+
+instance injectLeft :: Inject a b => Inject a (Either b c) where
+  inj = Left <<< inj
+  prj = either prj (const Nothing)
+
+else instance injectRight :: Inject a b => Inject a (Either c b) where
+  inj = Right <<< inj
+  prj = either (const Nothing) prj
+
+else instance injectReflexive :: Inject a a where
+  inj = id
+  prj = Just