Added optimized SortedMap.lookup/member/delete . NOT TESTED

plutus-tx/src/PlutusTx/SortedMap.hs

@@ -7,6 +7,7 @@
 {-# LANGUAGE TemplateHaskell       #-}
 {-# LANGUAGE UndecidableInstances  #-}
 {-# LANGUAGE ViewPatterns          #-}
+{-# LANGUAGE ScopedTypeVariables          #-}
 {-| This is like `PlutusTx.AssocMap` but with the extra invariant that the entries are kept
 sorted on the KEYS upon construction, insertion, and deletion.
 As with "PlutusTx.AssocMap", using the unsafe API may lead to duplicate entries, whereas using the
@@ -18,6 +19,7 @@ module PlutusTx.SortedMap
     , insert
     , delete
     , lookup
+    , member
     , minViewWithKey
     , isSortedDeDuped
     , isValid
@@ -126,14 +128,33 @@ empty :: SortedMap k v
 empty = SortedMap AssocMap.empty
 
 {-# INLINABLE delete #-}
--- OPTIMIZE: Using AssocMap.delete works, but a version that stops earlier would be better
-delete :: (Eq k) => k -> SortedMap k v -> SortedMap k v
-delete k = fromMapUnsafe . AssocMap.delete k . toMap
+delete :: forall k v. (Ord k) => k -> SortedMap k v -> SortedMap k v
+delete c (toList -> alist) = fromListUnsafe (go alist)
+  where
+    go [] = []
+    go ms@(hd@(c', _) : rest) = case c `compare` c' of
+                              LT -> hd : go rest
+                              EQ -> rest
+                              GT -> ms
+
+{-# INLINABLE member #-}
+-- | Is the key a member of the map?
+member :: forall k v. (Ord k) => k -> SortedMap k v -> Bool
+member k m = isJust (lookup k m)
 
 {-# INLINABLE lookup #-}
--- OPTIMIZE: a manual implementation can stop earlier than AssocMap.lookup, upon missing keys only
-lookup :: (Eq k) => k -> SortedMap k v -> Haskell.Maybe v
-lookup k = AssocMap.lookup k . toMap
+-- | Find an entry in a 'SortedMap'.
+lookup :: forall k v. (Tx.Ord k) => k -> SortedMap k v -> Haskell.Maybe v
+lookup c (toList -> alist) =
+  let
+    go :: [(k, v)] -> Maybe v
+    go []              = Nothing
+    go ((c', i) : xs') = case c `compare` c' of
+        LT -> go xs'
+        EQ -> Just i
+        GT -> Nothing
+   in
+    go alist
 
 {-# INLINABLE minViewWithKey #-}
 -- | Assumes that the SortedMap is valid.
@@ -154,8 +175,8 @@ insertInternal (k,v) = go
       go = \case
         [] -> [(k,v)]
         ms@((k',v'):ms') -> case k `compare` k' of
-            EQ -> (k,v) : ms'
             LT -> (k,v) : ms
+            EQ -> (k,v) : ms'
             GT -> (k',v') : go ms'
 
 {-# INLINABLE isSortedDeDuped #-}