Add index based OMap operations

Author: paluh

src/Data/Map/Ordered/OMap.purs

@@ -5,9 +5,14 @@ module Data.Map.Ordered.OMap
   , fromFoldable
   , fromFoldableWithIndex
   , insert
+  , insertAt
   , isEmpty
   , keys
+  , keyIndex
   , lookup
+  , moveLeft
+  , moveRight
+  , moveTo
   , singleton
   , toUnfoldable
   , unionWith
@@ -137,6 +142,15 @@ insert k v (OMap m) =
         unit
     ) -- Anonymous function wrapper added to delay computation of the default case
 
+keyIndex :: forall k v. Eq k => k -> OMap k v -> Maybe Int
+keyIndex k (OMap m) = Array.findIndex (eq k <<< fst) m
+
+insertAt :: forall k v. Ord k => Int -> k -> v -> OMap k v -> Maybe (OMap k v)
+insertAt i k v m = do
+  let
+    OMap m' = delete k m
+  OMap <$> Array.insertAt i (k /\ v) m'
+
 delete :: forall k v. Ord k => k -> OMap k v -> OMap k v
 delete k om = filterKeys ((/=) k) om
 
@@ -152,3 +166,16 @@ alter f k om = case mOldValue, mNewValue of
   mOldValue = lookup k om
 
   mNewValue = f mOldValue
+
+moveTo :: forall k v. Ord k => Int -> k -> OMap k v -> Maybe (OMap k v)
+moveTo i k m = do
+  v <- lookup k m
+  let
+    m' = delete k m
+  insertAt i k v m'
+
+moveLeft :: forall k v. Ord k => k -> OMap k v -> Maybe (OMap k v)
+moveLeft k m = keyIndex k m >>= \i -> moveTo (i - 1) k m
+
+moveRight :: forall k v. Ord k => k -> OMap k v -> Maybe (OMap k v)
+moveRight k m = keyIndex k m >>= \i -> moveTo (i + 1) k m

test/Data/Map/Ordered.purs

@@ -0,0 +1,34 @@
+module Data.Map.Ordered.Spec
+  ( orderedMapSpec
+  ) where
+
+import Prelude
+
+import Data.Map.Ordered.OMap (fromFoldable, moveLeft, moveRight)
+import Data.Maybe (Maybe(..))
+import Data.Tuple.Nested ((/\))
+import Test.Spec (Spec, describe, it)
+import Test.Spec.Assertions (shouldEqual)
+
+orderedMapSpec :: Spec Unit
+orderedMapSpec = do
+  describe "moveLeft" do
+    it "fails on the first element" do
+      let
+        m = fromFoldable [ "foo" /\ 1, "bar" /\ 2, "baz" /\ 3 ]
+      moveLeft "foo" m `shouldEqual` Nothing
+    it "moves the second element" do
+      let
+        m = fromFoldable [ "foo" /\ 1, "bar" /\ 2, "baz" /\ 3 ]
+      moveLeft "bar" m `shouldEqual`
+        (Just $ fromFoldable [ "bar" /\ 2, "foo" /\ 1, "baz" /\ 3 ])
+  describe "moveRight" do
+    it "fails on the last element" do
+      let
+        m = fromFoldable [ "foo" /\ 1, "bar" /\ 2, "baz" /\ 3 ]
+      moveRight "baz" m `shouldEqual` Nothing
+    it "moves the second element" do
+      let
+        m = fromFoldable [ "foo" /\ 1, "bar" /\ 2, "baz" /\ 3 ]
+      moveRight "bar" m `shouldEqual`
+        (Just $ fromFoldable [ "foo" /\ 1, "baz" /\ 3, "bar" /\ 2 ])

test/Main.purs

@@ -6,6 +6,7 @@ import Data.Array.Extra.Spec (arrayExtraSpec)
 import Data.BigInt.Argonaut.Spec (bigIntSpec)
 import Data.Cursor.Spec (cursorSpec)
 import Data.Foldable.Extra.Spec (foldableExtraSpec)
+import Data.Map.Ordered.Spec (orderedMapSpec)
 import Data.String.Extra.Spec (stringExtraSpec)
 import Effect (Effect)
 import Effect.Aff (launchAff_)
@@ -23,3 +24,4 @@ main =
       stringExtraSpec
       assocMapSpec
       bigIntSpec
+      orderedMapSpec