Merge pull request #44 from purescript/inj-reflexive

Reorder Inject instances to allow inj :: a -> a

Author: garyb

src/Data/Either/Inject.purs

@@ -9,14 +9,15 @@ class Inject a b where
   inj :: a -> b
   prj :: b -> Maybe a
 
-instance injectLeft :: Inject a (Either a b) where
+instance injectReflexive :: Inject a a where
+  inj = identity
+  prj = Just
+
+else instance injectLeft :: Inject a (Either a b) where
   inj = Left
   prj = either Just (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 = identity
-  prj = Just

test/Main.purs

@@ -26,6 +26,19 @@ main = do
     { actual: inj 100 :: MySum
     , expected: in3 100
     }
+  log "Test injection with the injectReflexive instance"
+  assertEqual
+    let
+      x = inj 100 :: MySum
+    in
+      { actual: inj x :: MySum
+      , expected: x
+      }
+  log "Test that injection picks the left-most option"
+  assertEqual
+    { actual: inj 100 :: Either3 Int Int Int
+    , expected: in1 100
+    }
   log "Test projection"
   assertEqual
     { actual: prj (in1 true :: MySum)