From 02f399759de0e711f6ae4983be2fc3d2f46579ef Mon Sep 17 00:00:00 2001
From: Alexandre Esteves <alexandre.fmp.esteves@gmail.com>
Date: Sun, 21 Jul 2019 01:32:31 +0100
Subject: [PATCH 1/5] Add 'compose' for maps

---
 containers-tests/tests/intmap-properties.hs   |  5 +++++
 containers-tests/tests/map-properties.hs      |  5 +++++
 containers/src/Data/IntMap/Internal.hs        | 22 +++++++++++++++++++
 containers/src/Data/IntMap/Lazy.hs            |  3 +++
 containers/src/Data/IntMap/Strict.hs          |  3 +++
 containers/src/Data/IntMap/Strict/Internal.hs | 22 +++++++++++++++++++
 containers/src/Data/Map/Internal.hs           | 22 +++++++++++++++++++
 containers/src/Data/Map/Lazy.hs               |  3 +++
 containers/src/Data/Map/Strict.hs             |  3 +++
 containers/src/Data/Map/Strict/Internal.hs    | 22 +++++++++++++++++++
 10 files changed, 110 insertions(+)

diff --git a/containers-tests/tests/intmap-properties.hs b/containers-tests/tests/intmap-properties.hs
index 86eb62764..99e784924 100644
--- a/containers-tests/tests/intmap-properties.hs
+++ b/containers-tests/tests/intmap-properties.hs
@@ -8,6 +8,7 @@ import Data.IntMap.Lazy as Data.IntMap hiding (showTree)
 import Data.IntMap.Internal.Debug (showTree)
 import IntMapValidity (valid)
 
+import Control.Monad ((>=>))
 import Data.Monoid
 import Data.Maybe hiding (mapMaybe)
 import qualified Data.Maybe as Maybe (mapMaybe)
@@ -163,6 +164,7 @@ main = defaultMain
              , testProperty "lookupLE"             prop_lookupLE
              , testProperty "lookupGE"             prop_lookupGE
              , testProperty "disjoint"             prop_disjoint
+             , testProperty "compose"              prop_compose
              , testProperty "lookupMin"            prop_lookupMin
              , testProperty "lookupMax"            prop_lookupMax
              , testProperty "findMin"              prop_findMin
@@ -884,6 +886,9 @@ prop_intersectionWithKeyModel xs ys
 prop_disjoint :: UMap -> UMap -> Property
 prop_disjoint m1 m2 = disjoint m1 m2 === null (intersection m1 m2)
 
+prop_compose :: IMap -> IMap -> Int -> Property
+prop_compose bc ab k = (compose bc ab !? k) === (flip lookup ab >=> flip lookup bc) k
+
 -- TODO: the second argument should be simply an 'IntSet', but that
 -- runs afoul of our orphan instance.
 prop_restrictKeys :: IMap -> IMap -> Property
diff --git a/containers-tests/tests/map-properties.hs b/containers-tests/tests/map-properties.hs
index c1bff0168..48ca9dfef 100644
--- a/containers-tests/tests/map-properties.hs
+++ b/containers-tests/tests/map-properties.hs
@@ -11,6 +11,7 @@ import Data.Map.Internal (Map (..), link2, link, bin)
 import Data.Map.Internal.Debug (showTree, showTreeWith, balanced)
 
 import Control.Applicative (Const(Const, getConst), pure, (<$>), (<*>))
+import Control.Monad ((>=>))
 import Data.Functor.Identity (Identity(runIdentity))
 import Data.Monoid
 import Data.Maybe hiding (mapMaybe)
@@ -173,6 +174,7 @@ main = defaultMain
          , testProperty "intersectionWithKey"  prop_intersectionWithKey
          , testProperty "intersectionWithKeyModel" prop_intersectionWithKeyModel
          , testProperty "disjoint"             prop_disjoint
+         , testProperty "compose"              prop_compose
          , testProperty "differenceMerge"   prop_differenceMerge
          , testProperty "unionWithKeyMerge"   prop_unionWithKeyMerge
          , testProperty "mergeWithKey model"   prop_mergeWithKeyModel
@@ -1074,6 +1076,9 @@ prop_intersectionWithKeyModel xs ys
 prop_disjoint :: UMap -> UMap -> Property
 prop_disjoint m1 m2 = disjoint m1 m2 === null (intersection m1 m2)
 
+prop_compose :: IMap -> IMap -> Int -> Property
+prop_compose bc ab k = (compose bc ab !? k) === (flip lookup ab >=> flip lookup bc) k
+
 prop_mergeWithKeyModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
 prop_mergeWithKeyModel xs ys
   = and [ testMergeWithKey f keep_x keep_y
diff --git a/containers/src/Data/IntMap/Internal.hs b/containers/src/Data/IntMap/Internal.hs
index 9cf26968a..8ab212a12 100644
--- a/containers/src/Data/IntMap/Internal.hs
+++ b/containers/src/Data/IntMap/Internal.hs
@@ -131,6 +131,9 @@ module Data.IntMap.Internal (
     , intersectionWith
     , intersectionWithKey
 
+    -- ** Compose
+    , compose
+
     -- ** General combining function
     , SimpleWhenMissing
     , SimpleWhenMatched
@@ -761,6 +764,25 @@ disjoint t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
               | zero p1 m2       = disjoint t1 l2
               | otherwise        = disjoint t1 r2
 
+{--------------------------------------------------------------------
+  Compose
+--------------------------------------------------------------------}
+-- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
+-- the other, by using the values of the former as keys for lookups
+-- on the later.
+--
+-- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
+--
+-- @
+-- ('compose' bc ab '!?') = (bc '!?') <=< (ab '!?')
+-- @
+--
+-- @since UNRELEASED
+compose :: IntMap c -> IntMap Int -> IntMap c
+compose bc ab = if null bc
+                then empty
+                else mapMaybe (bc !?) ab
+
 {--------------------------------------------------------------------
   Construction
 --------------------------------------------------------------------}
diff --git a/containers/src/Data/IntMap/Lazy.hs b/containers/src/Data/IntMap/Lazy.hs
index 8d4ce8c82..3f38e3c29 100644
--- a/containers/src/Data/IntMap/Lazy.hs
+++ b/containers/src/Data/IntMap/Lazy.hs
@@ -146,6 +146,9 @@ module Data.IntMap.Lazy (
     -- ** Disjoint
     , disjoint
 
+    -- ** Compose
+    , compose
+
     -- ** Universal combining function
     , mergeWithKey
 
diff --git a/containers/src/Data/IntMap/Strict.hs b/containers/src/Data/IntMap/Strict.hs
index ef732c2e2..36bbad1e2 100644
--- a/containers/src/Data/IntMap/Strict.hs
+++ b/containers/src/Data/IntMap/Strict.hs
@@ -165,6 +165,9 @@ module Data.IntMap.Strict (
     -- ** Disjoint
     , disjoint
 
+    -- ** Compose
+    , compose
+
     -- ** Universal combining function
     , mergeWithKey
 
diff --git a/containers/src/Data/IntMap/Strict/Internal.hs b/containers/src/Data/IntMap/Strict/Internal.hs
index e7345418f..5e7b94b52 100644
--- a/containers/src/Data/IntMap/Strict/Internal.hs
+++ b/containers/src/Data/IntMap/Strict/Internal.hs
@@ -162,6 +162,9 @@ module Data.IntMap.Strict.Internal (
     -- ** Disjoint
     , disjoint
 
+    -- ** Compose
+    , compose
+
     -- ** Universal combining function
     , mergeWithKey
 
@@ -717,6 +720,25 @@ intersectionWithKey :: (Key -> a -> b -> c) -> IntMap a -> IntMap b -> IntMap c
 intersectionWithKey f m1 m2
   = mergeWithKey' bin (\(Tip k1 x1) (Tip _k2 x2) -> Tip k1 $! f k1 x1 x2) (const Nil) (const Nil) m1 m2
 
+{--------------------------------------------------------------------
+  Compose
+--------------------------------------------------------------------}
+-- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
+-- the other, by using the values of the former as keys for lookups
+-- on the later.
+--
+-- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
+--
+-- @
+-- ('compose' bc ab '!?') = (bc '!?') <=< (ab '!?')
+-- @
+--
+-- @since UNRELEASED
+compose :: IntMap c -> IntMap Int -> IntMap c
+compose bc ab = if null bc
+                then empty
+                else mapMaybe (bc !?) ab
+
 {--------------------------------------------------------------------
   MergeWithKey
 --------------------------------------------------------------------}
diff --git a/containers/src/Data/Map/Internal.hs b/containers/src/Data/Map/Internal.hs
index 32c4e08bc..7b89d21c4 100644
--- a/containers/src/Data/Map/Internal.hs
+++ b/containers/src/Data/Map/Internal.hs
@@ -192,6 +192,9 @@ module Data.Map.Internal (
     -- ** Disjoint
     , disjoint
 
+    -- ** Compose
+    , compose
+
     -- ** General combining function
     , SimpleWhenMissing
     , SimpleWhenMatched
@@ -2085,6 +2088,25 @@ disjoint (Bin _ k _ l r) t
   where
     (lt,found,gt) = splitMember k t
 
+{--------------------------------------------------------------------
+  Compose
+--------------------------------------------------------------------}
+-- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
+-- the other, by using the values of the former as keys for lookups
+-- on the later.
+--
+-- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
+--
+-- @
+-- ('compose' bc ab '!?') = (bc '!?') <=< (ab '!?')
+-- @
+--
+-- @since UNRELEASED
+compose :: Ord b => Map b c -> Map a b -> Map a c
+compose bc ab = if null bc
+                then empty
+                else mapMaybe (bc !?) ab
+
 #if !MIN_VERSION_base (4,8,0)
 -- | The identity type.
 newtype Identity a = Identity { runIdentity :: a }
diff --git a/containers/src/Data/Map/Lazy.hs b/containers/src/Data/Map/Lazy.hs
index 37ae931e6..6b05603a1 100644
--- a/containers/src/Data/Map/Lazy.hs
+++ b/containers/src/Data/Map/Lazy.hs
@@ -166,6 +166,9 @@ module Data.Map.Lazy (
     -- ** Disjoint
     , disjoint
 
+    -- ** Compose
+    , compose
+
     -- ** General combining functions
     -- | See "Data.Map.Merge.Lazy"
 
diff --git a/containers/src/Data/Map/Strict.hs b/containers/src/Data/Map/Strict.hs
index a73078413..8eea8c329 100644
--- a/containers/src/Data/Map/Strict.hs
+++ b/containers/src/Data/Map/Strict.hs
@@ -182,6 +182,9 @@ module Data.Map.Strict
     -- ** Disjoint
     , disjoint
 
+    -- ** Compose
+    , compose
+
     -- ** General combining functions
     -- | See "Data.Map.Merge.Strict"
 
diff --git a/containers/src/Data/Map/Strict/Internal.hs b/containers/src/Data/Map/Strict/Internal.hs
index a161b2f49..b71c9a223 100644
--- a/containers/src/Data/Map/Strict/Internal.hs
+++ b/containers/src/Data/Map/Strict/Internal.hs
@@ -145,6 +145,9 @@ module Data.Map.Strict.Internal
     -- ** Disjoint
     , disjoint
 
+    -- ** Compose
+    , compose
+
     -- ** General combining function
     , SimpleWhenMissing
     , SimpleWhenMatched
@@ -1200,6 +1203,25 @@ forceMaybe Nothing = Nothing
 forceMaybe m@(Just !_) = m
 {-# INLINE forceMaybe #-}
 
+{--------------------------------------------------------------------
+  Compose
+--------------------------------------------------------------------}
+-- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
+-- the other, by using the values of the former as keys for lookups
+-- on the later.
+--
+-- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
+--
+-- @
+-- ('compose' bc ab '!?') = (bc '!?') <=< (ab '!?')
+-- @
+--
+-- @since UNRELEASED
+compose :: Ord b => Map b c -> Map a b -> Map a c
+compose bc ab = if null bc
+                then empty
+                else mapMaybe (bc !?) ab
+
 {--------------------------------------------------------------------
   MergeWithKey
 --------------------------------------------------------------------}

From a7534a9640896f610ffcdf6e61766b7e2920c008 Mon Sep 17 00:00:00 2001
From: Alexandre Esteves <alexandre.fmp.esteves@gmail.com>
Date: Mon, 14 Oct 2019 10:01:12 +0100
Subject: [PATCH 2/5] Fix typos

---
 containers/src/Data/IntMap/Internal.hs        | 2 +-
 containers/src/Data/IntMap/Strict/Internal.hs | 2 +-
 containers/src/Data/Map/Internal.hs           | 2 +-
 containers/src/Data/Map/Strict/Internal.hs    | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/containers/src/Data/IntMap/Internal.hs b/containers/src/Data/IntMap/Internal.hs
index 8ab212a12..4293fbe1a 100644
--- a/containers/src/Data/IntMap/Internal.hs
+++ b/containers/src/Data/IntMap/Internal.hs
@@ -769,7 +769,7 @@ disjoint t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
 --------------------------------------------------------------------}
 -- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
 -- the other, by using the values of the former as keys for lookups
--- on the later.
+-- in the latter.
 --
 -- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
 --
diff --git a/containers/src/Data/IntMap/Strict/Internal.hs b/containers/src/Data/IntMap/Strict/Internal.hs
index 5e7b94b52..c8845d5b3 100644
--- a/containers/src/Data/IntMap/Strict/Internal.hs
+++ b/containers/src/Data/IntMap/Strict/Internal.hs
@@ -725,7 +725,7 @@ intersectionWithKey f m1 m2
 --------------------------------------------------------------------}
 -- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
 -- the other, by using the values of the former as keys for lookups
--- on the later.
+-- in the latter.
 --
 -- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
 --
diff --git a/containers/src/Data/Map/Internal.hs b/containers/src/Data/Map/Internal.hs
index 7b89d21c4..2f9f21fad 100644
--- a/containers/src/Data/Map/Internal.hs
+++ b/containers/src/Data/Map/Internal.hs
@@ -2093,7 +2093,7 @@ disjoint (Bin _ k _ l r) t
 --------------------------------------------------------------------}
 -- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
 -- the other, by using the values of the former as keys for lookups
--- on the later.
+-- in the latter.
 --
 -- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
 --
diff --git a/containers/src/Data/Map/Strict/Internal.hs b/containers/src/Data/Map/Strict/Internal.hs
index b71c9a223..82c879739 100644
--- a/containers/src/Data/Map/Strict/Internal.hs
+++ b/containers/src/Data/Map/Strict/Internal.hs
@@ -1208,7 +1208,7 @@ forceMaybe m@(Just !_) = m
 --------------------------------------------------------------------}
 -- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
 -- the other, by using the values of the former as keys for lookups
--- on the later.
+-- in the latter.
 --
 -- > compose (fromList [('a', "A"), ('b', "B")]) (fromList [(1,'a'),(2,'b'),(3,'z')]) = fromList [(1,"A"),(2,"B")]
 --

From db55ad473f656765d757fde82ace804b168dd348 Mon Sep 17 00:00:00 2001
From: Alexandre Esteves <alexandre.fmp.esteves@gmail.com>
Date: Mon, 14 Oct 2019 10:04:41 +0100
Subject: [PATCH 3/5] Cleanup

---
 containers-tests/tests/intmap-properties.hs | 4 ++--
 containers-tests/tests/map-properties.hs    | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/containers-tests/tests/intmap-properties.hs b/containers-tests/tests/intmap-properties.hs
index 99e784924..e47e494b5 100644
--- a/containers-tests/tests/intmap-properties.hs
+++ b/containers-tests/tests/intmap-properties.hs
@@ -8,7 +8,7 @@ import Data.IntMap.Lazy as Data.IntMap hiding (showTree)
 import Data.IntMap.Internal.Debug (showTree)
 import IntMapValidity (valid)
 
-import Control.Monad ((>=>))
+import Control.Monad ((<=<))
 import Data.Monoid
 import Data.Maybe hiding (mapMaybe)
 import qualified Data.Maybe as Maybe (mapMaybe)
@@ -887,7 +887,7 @@ prop_disjoint :: UMap -> UMap -> Property
 prop_disjoint m1 m2 = disjoint m1 m2 === null (intersection m1 m2)
 
 prop_compose :: IMap -> IMap -> Int -> Property
-prop_compose bc ab k = (compose bc ab !? k) === (flip lookup ab >=> flip lookup bc) k
+prop_compose bc ab k = (compose bc ab !? k) === ((bc !?) <=< (ab !?)) k
 
 -- TODO: the second argument should be simply an 'IntSet', but that
 -- runs afoul of our orphan instance.
diff --git a/containers-tests/tests/map-properties.hs b/containers-tests/tests/map-properties.hs
index 48ca9dfef..9f81c42c0 100644
--- a/containers-tests/tests/map-properties.hs
+++ b/containers-tests/tests/map-properties.hs
@@ -11,7 +11,7 @@ import Data.Map.Internal (Map (..), link2, link, bin)
 import Data.Map.Internal.Debug (showTree, showTreeWith, balanced)
 
 import Control.Applicative (Const(Const, getConst), pure, (<$>), (<*>))
-import Control.Monad ((>=>))
+import Control.Monad ((<=<))
 import Data.Functor.Identity (Identity(runIdentity))
 import Data.Monoid
 import Data.Maybe hiding (mapMaybe)
@@ -1077,7 +1077,7 @@ prop_disjoint :: UMap -> UMap -> Property
 prop_disjoint m1 m2 = disjoint m1 m2 === null (intersection m1 m2)
 
 prop_compose :: IMap -> IMap -> Int -> Property
-prop_compose bc ab k = (compose bc ab !? k) === (flip lookup ab >=> flip lookup bc) k
+prop_compose bc ab k = (compose bc ab !? k) === ((bc !?) <=< (ab !?)) k
 
 prop_mergeWithKeyModel :: [(Int,Int)] -> [(Int,Int)] -> Bool
 prop_mergeWithKeyModel xs ys

From 0c5c1e18cb96c170e1507dcf212f49ca6287e947 Mon Sep 17 00:00:00 2001
From: Alexandre Esteves <alexandre.fmp.esteves@gmail.com>
Date: Sun, 22 Dec 2019 22:52:31 +0000
Subject: [PATCH 4/5] Force second argument of 'compose'

---
 containers/src/Data/IntMap/Internal.hs        | 6 +++---
 containers/src/Data/IntMap/Strict/Internal.hs | 6 +++---
 containers/src/Data/Map/Internal.hs           | 6 +++---
 containers/src/Data/Map/Strict/Internal.hs    | 6 +++---
 4 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/containers/src/Data/IntMap/Internal.hs b/containers/src/Data/IntMap/Internal.hs
index 4293fbe1a..e0d572482 100644
--- a/containers/src/Data/IntMap/Internal.hs
+++ b/containers/src/Data/IntMap/Internal.hs
@@ -779,9 +779,9 @@ disjoint t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
 --
 -- @since UNRELEASED
 compose :: IntMap c -> IntMap Int -> IntMap c
-compose bc ab = if null bc
-                then empty
-                else mapMaybe (bc !?) ab
+compose bc !ab
+  | null bc = empty
+  | otherwise = mapMaybe (bc !?) ab
 
 {--------------------------------------------------------------------
   Construction
diff --git a/containers/src/Data/IntMap/Strict/Internal.hs b/containers/src/Data/IntMap/Strict/Internal.hs
index c8845d5b3..e7739d678 100644
--- a/containers/src/Data/IntMap/Strict/Internal.hs
+++ b/containers/src/Data/IntMap/Strict/Internal.hs
@@ -735,9 +735,9 @@ intersectionWithKey f m1 m2
 --
 -- @since UNRELEASED
 compose :: IntMap c -> IntMap Int -> IntMap c
-compose bc ab = if null bc
-                then empty
-                else mapMaybe (bc !?) ab
+compose bc !ab
+  | null bc = empty
+  | otherwise = mapMaybe (bc !?) ab
 
 {--------------------------------------------------------------------
   MergeWithKey
diff --git a/containers/src/Data/Map/Internal.hs b/containers/src/Data/Map/Internal.hs
index 2f9f21fad..879c6933a 100644
--- a/containers/src/Data/Map/Internal.hs
+++ b/containers/src/Data/Map/Internal.hs
@@ -2103,9 +2103,9 @@ disjoint (Bin _ k _ l r) t
 --
 -- @since UNRELEASED
 compose :: Ord b => Map b c -> Map a b -> Map a c
-compose bc ab = if null bc
-                then empty
-                else mapMaybe (bc !?) ab
+compose bc !ab
+  | null bc = empty
+  | otherwise = mapMaybe (bc !?) ab
 
 #if !MIN_VERSION_base (4,8,0)
 -- | The identity type.
diff --git a/containers/src/Data/Map/Strict/Internal.hs b/containers/src/Data/Map/Strict/Internal.hs
index 82c879739..450dc0976 100644
--- a/containers/src/Data/Map/Strict/Internal.hs
+++ b/containers/src/Data/Map/Strict/Internal.hs
@@ -1218,9 +1218,9 @@ forceMaybe m@(Just !_) = m
 --
 -- @since UNRELEASED
 compose :: Ord b => Map b c -> Map a b -> Map a c
-compose bc ab = if null bc
-                then empty
-                else mapMaybe (bc !?) ab
+compose bc !ab
+  | null bc = empty
+  | otherwise = mapMaybe (bc !?) ab
 
 {--------------------------------------------------------------------
   MergeWithKey

From 2bf99eb833f031e1592e2990b3b0bbaeca9f10f8 Mon Sep 17 00:00:00 2001
From: Alexandre Esteves <alexandre.fmp.esteves@gmail.com>
Date: Sun, 22 Dec 2019 22:57:08 +0000
Subject: [PATCH 5/5] Fix bounds

---
 containers/src/Data/IntMap/Internal.hs        | 2 +-
 containers/src/Data/IntMap/Strict/Internal.hs | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/containers/src/Data/IntMap/Internal.hs b/containers/src/Data/IntMap/Internal.hs
index e0d572482..65444511f 100644
--- a/containers/src/Data/IntMap/Internal.hs
+++ b/containers/src/Data/IntMap/Internal.hs
@@ -767,7 +767,7 @@ disjoint t1@(Bin p1 m1 l1 r1) t2@(Bin p2 m2 l2 r2)
 {--------------------------------------------------------------------
   Compose
 --------------------------------------------------------------------}
--- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
+-- | /O(|ab|*min(|bc|,W))/. Relate the keys of one map to the values of
 -- the other, by using the values of the former as keys for lookups
 -- in the latter.
 --
diff --git a/containers/src/Data/IntMap/Strict/Internal.hs b/containers/src/Data/IntMap/Strict/Internal.hs
index e7739d678..e3bc76d98 100644
--- a/containers/src/Data/IntMap/Strict/Internal.hs
+++ b/containers/src/Data/IntMap/Strict/Internal.hs
@@ -723,7 +723,7 @@ intersectionWithKey f m1 m2
 {--------------------------------------------------------------------
   Compose
 --------------------------------------------------------------------}
--- | /O(|ab|*log(|bc|))/. Relate the keys of one map to the values of
+-- | /O(|ab|*min(|bc|,W))/. Relate the keys of one map to the values of
 -- the other, by using the values of the former as keys for lookups
 -- in the latter.
 --