diff --git a/library/Timestamp/Foldls.hs b/library/Timestamp/Foldls.hs
new file mode 100644
--- /dev/null
+++ b/library/Timestamp/Foldls.hs
@@ -0,0 +1,30 @@
+{-|
+Folds on timestamped values
+-}
+module Timestamp.Foldl
+where
+
+import Timestamp.Prelude hiding (maximum)
+import Timestamp
+import Control.Foldl
+
+
+untimestamped :: Fold input output -> Fold (Timestamped input) output
+untimestamped =
+  premap (\ (Timestamped _ x) -> x)
+
+filteringByUtcTime :: (UTCTime -> Bool) -> Fold (Timestamped input) output -> Fold (Timestamped input) output
+filteringByUtcTime filter =
+  filteringByTimestamp (filter . timestampUtcTime)
+
+filteringByTimestamp :: (Timestamp -> Bool) -> Fold (Timestamped input) output -> Fold (Timestamped input) output
+filteringByTimestamp filter =
+  prefilter (\ (Timestamped ts _) -> filter ts)
+
+inUtcTimeRange :: UTCTime -> UTCTime -> Fold (Timestamped input) output -> Fold (Timestamped input) output
+inUtcTimeRange start end =
+  inTimestampRange (utcTimeTimestamp start) (utcTimeTimestamp end)
+
+inTimestampRange :: Timestamp -> Timestamp -> Fold (Timestamped input) output -> Fold (Timestamped input) output
+inTimestampRange start end =
+  filteringByTimestamp (\ ts -> ts >= start && ts < end)
diff --git a/library/Timestamp/Prelude.hs b/library/Timestamp/Prelude.hs
--- a/library/Timestamp/Prelude.hs
+++ b/library/Timestamp/Prelude.hs
@@ -69,6 +69,10 @@
 import Text.Read as Exports (Read(..), readMaybe, readEither)
 import Unsafe.Coerce as Exports
 
+-- foldl
+-------------------------
+import Control.Foldl as Exports (Fold(..), FoldM(..))
+
 -- cereal
 -------------------------
 import Data.Serialize as Exports (Serialize)
diff --git a/timestamp.cabal b/timestamp.cabal
--- a/timestamp.cabal
+++ b/timestamp.cabal
@@ -1,7 +1,7 @@
 name:
   timestamp
 version:
-  0.1.0.1
+  0.1.1
 synopsis:
   Space-efficient Unix timestamp and utilities
 category:
@@ -40,12 +40,14 @@
     Haskell2010
   exposed-modules:
     Timestamp
+    Timestamp.Foldls
   other-modules:
     Timestamp.Data.Conversion
     Timestamp.Data.TypesAndInstances
     Timestamp.Prelude
   build-depends:
     cereal >=0.5.4 && <0.6,
+    foldl >=1.3.5 && <2,
     hashable >=1.2 && <2,
     QuickCheck >=2.8.1 && <3,
     time >=1.8 && <2,