Call it PatchOrReplacement instead of Patchable

Author: Ericson2314

patch.cabal

@@ -57,7 +57,7 @@ library
                  , Data.Patch.Map
                  , Data.Patch.MapWithMove
                  , Data.Patch.MapWithPatchingMove
-                 , Data.Patch.Patchable
+                 , Data.Patch.PatchOrReplacement
                  , Data.Semigroup.Additive
 
   ghc-options: -Wall -fwarn-redundant-constraints -fwarn-tabs

src/Data/Patch/PatchOrReplacement.hs

@@ -0,0 +1,46 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+module Data.Patch.PatchOrReplacement where
+
+import Data.Patch
+#if !MIN_VERSION_base(4,11,0)
+import Data.Semigroup (Semigroup (..))
+#endif
+import GHC.Generics
+
+-- | Like SemiMap/PartialMap but for anything patchable
+data PatchOrReplacement p
+  = PatchOrReplacement_Patch p
+  | PatchOrReplacement_Complete (PatchTarget p)
+  deriving (Generic)
+
+deriving instance (Eq p, Eq (PatchTarget p)) => Eq (PatchOrReplacement p)
+deriving instance (Ord p, Ord (PatchTarget p)) => Ord (PatchOrReplacement p)
+deriving instance (Show p, Show (PatchTarget p)) => Show (PatchOrReplacement p)
+deriving instance (Read p, Read (PatchTarget p)) => Read (PatchOrReplacement p)
+
+completePatchOrReplacement :: PatchOrReplacement p -> Maybe (PatchTarget p)
+completePatchOrReplacement = \case
+  PatchOrReplacement_Complete t -> Just t
+  PatchOrReplacement_Patch _ -> Nothing
+
+instance ( Monoid p
+#if !MIN_VERSION_base(4,11,0)
+         , Semigroup p
+#endif
+         , Patch p
+         ) => Monoid (PatchOrReplacement p) where
+  mempty = PatchOrReplacement_Patch mempty
+  mappend = (<>)
+
+instance (Semigroup p, Patch p) => Semigroup (PatchOrReplacement p) where
+  (<>) = curry $ \case
+    (PatchOrReplacement_Patch a, PatchOrReplacement_Patch b) -> PatchOrReplacement_Patch $ a <> b
+    (PatchOrReplacement_Patch a, PatchOrReplacement_Complete b) -> PatchOrReplacement_Complete $ applyAlways a b
+    (PatchOrReplacement_Complete a, _) -> PatchOrReplacement_Complete a