Add append

src/JRec.hs

@@ -4,10 +4,11 @@
 
 module JRec
   ( unField,
-    union,
     (:=) (..),
     Rec,
     pattern Rec,
+    append,
+    union,
   )
 where
 
@@ -39,7 +40,24 @@ unField _ (_ R.:= value) = value
 -- Other operations
 ----------------------------------------------------------------------------
 
--- Append records
+-- Appends records, without removing duplicates.
+--
+-- Left-biased. Does not sort.
+append ::
+  forall lhs rhs res.
+  ( KnownNat (R.RecSize lhs),
+    KnownNat (R.RecSize rhs),
+    KnownNat (R.RecSize lhs + R.RecSize rhs),
+    res ~ R.RecAppend lhs rhs,
+    R.RecCopy lhs lhs res,
+    R.RecCopy rhs rhs res
+  ) =>
+  Rec lhs ->
+  Rec rhs ->
+  Rec res
+append = R.combine
+
+-- Merges records, removing duplicates (TODO)
 --
 -- Left-biased. Does not sort.
 --

test/JRecSpec.hs

@@ -39,6 +39,15 @@ spec = do
       `shouldBe` (Rec (#u := True, #a := 8))
     setA2 (Rec (#u := True, #a := 5, #b := 6))
       `shouldBe` (Rec (#u := True, #a := 8, #b := 6))
+  describe "append" $ do
+    it "simple append" $ do
+      Rec (#a := 1) `append` Rec (#b := 2)
+        `shouldBe` Rec (#a := 1, #b := 2)
+    it "append with duplicates" $ do
+      let r1 = Rec (#b := 5, #a := 6)
+          r2 = Rec (#c := 7, #a := 8)
+      r1 `union` r2
+        `shouldBe` Rec (#b := 5, #a := 8, #c := 7, #a := 8)
   describe "union" $ do
     it "simple union" $ do
       Rec (#a := 1) `union` Rec (#b := 2)