diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+1.5.0.0 [2024-12-23]
+--------------------
+* Mini.Data.{Map,Set}:
+  * Simplify 'show'
+  * Fix element processing order of folds
+* Mini.Transformers.ParserT:
+  * Add combinator 'annotate'
+
 1.4.3.0 [2024-12-08]
 --------------------
 * All transformers now instantiate:
diff --git a/Mini/Data/Map.hs b/Mini/Data/Map.hs
--- a/Mini/Data/Map.hs
+++ b/Mini/Data/Map.hs
@@ -57,11 +57,9 @@
 ) where
 
 import Control.Applicative (
+  liftA2,
   (<|>),
  )
-import Control.Monad (
-  liftM2,
- )
 import Data.Bool (
   bool,
  )
@@ -138,15 +136,7 @@
   compare t1 t2 = compare (toAscList t1) (toAscList t2)
 
 instance (Show k, Show a) => Show (Map k a) where
-  show = curl . map [] go go go
-   where
-    go _ k a _ recl recr = recl <> show (k, a) <> "," <> recr
-    curl = wrap "{" "}" . removeTrailingComma
-    wrap open close s = open <> s <> close
-    removeTrailingComma s = case s of
-      [] -> []
-      [_] -> []
-      (c : cs) -> c : removeTrailingComma cs
+  show = show . toAscList
 
 instance Functor (Map k) where
   fmap f = map E (go L) (go B) (go R)
@@ -229,7 +219,7 @@
 
 -- | /O(m log n)/ Unite a map with another via left-biased key matching
 union :: (Ord k) => Map k a -> Map k a -> Map k a
-union t = foldrWithKey (\k a b -> bool (insert k a b) b $ k `member` t) t
+union = flip $ foldrWithKey insert
 
 {-
  - Conversion
@@ -237,11 +227,11 @@
 
 -- | /O(n)/ Turn a map into a list of @(key, value)@ pairs in ascending order
 toAscList :: Map k a -> [(k, a)]
-toAscList = foldlWithKey (\b k a -> (k, a) : b) []
+toAscList = foldrWithKey (\k a b -> (k, a) : b) []
 
 -- | /O(n)/ Turn a map into a list of @(key, value)@ pairs in descending order
 toDescList :: Map k a -> [(k, a)]
-toDescList = foldrWithKey (\k a b -> (k, a) : b) []
+toDescList = foldlWithKey (\b k a -> (k, a) : b) []
 
 {-
  - Fold
@@ -251,13 +241,13 @@
 foldlWithKey :: (b -> k -> a -> b) -> b -> Map k a -> b
 foldlWithKey f b = map b go go go
  where
-  go l k a _ _ recr = foldlWithKey f (f recr k a) l
+  go _ k a r recl _ = foldlWithKey f (f recl k a) r
 
 -- | /O(n)/ Reduce a map with a right-associative operation and an accumulator
 foldrWithKey :: (k -> a -> b -> b) -> b -> Map k a -> b
 foldrWithKey f b = map b go go go
  where
-  go _ k a r recl _ = foldrWithKey f (f k a recl) r
+  go l k a _ _ recr = foldrWithKey f (f k a recr) l
 
 {-
  - Modification
@@ -1091,7 +1081,7 @@
 
 -- | /O(n)/ Check whether a map is internally height-balanced and ordered
 valid :: (Ord k) => Map k a -> Bool
-valid = liftM2 (&&) balanced ordered
+valid = liftA2 (&&) balanced ordered
  where
   balanced =
     map
diff --git a/Mini/Data/Set.hs b/Mini/Data/Set.hs
--- a/Mini/Data/Set.hs
+++ b/Mini/Data/Set.hs
@@ -39,11 +39,9 @@
 ) where
 
 import Control.Applicative (
+  liftA2,
   (<|>),
  )
-import Control.Monad (
-  liftM2,
- )
 import Data.Bifunctor (
   first,
  )
@@ -113,19 +111,12 @@
   compare t1 t2 = compare (toAscList t1) (toAscList t2)
 
 instance (Show a) => Show (Set a) where
-  show = curl . set [] go go go
-   where
-    go _ a _ recl recr = recl <> show a <> "," <> recr
-    curl = wrap "{" "}" . removeTrailingComma
-    wrap open close s = open <> s <> close
-    removeTrailingComma [] = []
-    removeTrailingComma "," = []
-    removeTrailingComma (c : cs) = c : removeTrailingComma cs
+  show = show . toAscList
 
 instance Foldable Set where
   foldr f b = set b go go go
    where
-    go _ a r recl _ = foldr f (f a recl) r
+    go l a _ _ recr = foldr f (f a recr) l
 
 instance (Ord a) => Semigroup (Set a) where
   (<>) = union
@@ -181,11 +172,15 @@
 
 -- | /O(m log n)/ Intersect a set with another
 intersection :: (Ord a) => Set a -> Set a -> Set a
-intersection t = foldr (\a b -> bool b (insert a b) (a `member` t)) empty
+intersection t1 t2 =
+  foldr
+    (\a b -> bool b (insert a b) (a `member` t2))
+    empty
+    t1
 
 -- | /O(m log n)/ Unite a set with another
 union :: (Ord a) => Set a -> Set a -> Set a
-union = foldr insert
+union = flip $ foldr insert
 
 {-
  - Conversion
@@ -193,11 +188,11 @@
 
 -- | /O(n)/ Turn a set into a list of elements in ascending order
 toAscList :: Set a -> [a]
-toAscList = foldl (flip (:)) []
+toAscList = foldr (:) []
 
 -- | /O(n)/ Turn a set into a list of elements in descending order
 toDescList :: Set a -> [a]
-toDescList = foldr (:) []
+toDescList = foldl (flip (:)) []
 
 {-
  - Modification
@@ -872,7 +867,7 @@
 
 -- | /O(n)/ Check whether a set is internally height-balanced and ordered
 valid :: (Ord a) => Set a -> Bool
-valid = liftM2 (&&) balanced ordered
+valid = liftA2 (&&) balanced ordered
  where
   balanced =
     set
diff --git a/Mini/Transformers/ParserT.hs b/Mini/Transformers/ParserT.hs
--- a/Mini/Transformers/ParserT.hs
+++ b/Mini/Transformers/ParserT.hs
@@ -37,6 +37,7 @@
   accept,
   findFirst,
   findLast,
+  annotate,
 ) where
 
 import Control.Applicative (
@@ -273,3 +274,12 @@
 -- | Find and parse the last instance of @p@ via @findLast p@
 findLast :: (Monad m, Eq s, Show s) => ParserT s m a -> ParserT s m a
 findLast p = findFirst p >>= flip option (findLast p)
+
+-- | Prepend an error message to that of a parser
+annotate :: (Monad m) => String -> ParserT s m a -> ParserT s m a
+annotate s p =
+  ParserT $
+    runParserT p
+      >=> either
+        (pure . Left . ParseError . (s <>) . unexpected)
+        (pure . Right)
diff --git a/mini.cabal b/mini.cabal
--- a/mini.cabal
+++ b/mini.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.0
 name:               mini
-version:            1.4.3.0
+version:            1.5.0.0
 license:            MIT
 license-file:       LICENSE
 author:             Victor Wallsten <victor.wallsten@protonmail.com>