diff --git a/numhask-space.cabal b/numhask-space.cabal
--- a/numhask-space.cabal
+++ b/numhask-space.cabal
@@ -1,5 +1,5 @@
 name: numhask-space
-version: 0.3.0
+version: 0.3.1
 synopsis:
   numerical spaces
 description:
diff --git a/src/NumHask/Space/Histogram.hs b/src/NumHask/Space/Histogram.hs
--- a/src/NumHask/Space/Histogram.hs
+++ b/src/NumHask/Space/Histogram.hs
@@ -1,5 +1,4 @@
 {-# LANGUAGE DataKinds #-}
-{-# LANGUAGE TupleSections #-}
 {-# OPTIONS_GHC -Wall #-}
 
 -- | A histogram, if you squint, is a series of contiguous ranges, annotated with values.
@@ -7,6 +6,7 @@
   ( Histogram (..),
     DealOvers (..),
     fill,
+    cutI,
     regular,
     makeRects,
     regularQuantiles,
@@ -17,6 +17,8 @@
 where
 
 import qualified Control.Foldl as L
+import Data.Bool
+import Data.Foldable
 import qualified Data.List
 import qualified Data.Map as Map
 import Data.Maybe
@@ -43,15 +45,15 @@
 --
 -- >>> fill [0,50,100] [1..100]
 -- Histogram {cuts = [0.0,50.0,100.0], values = fromList [(1,50.0),(2,50.0)]}
-fill :: (Functor f, Foldable f) => [Double] -> f Double -> Histogram
-fill cs xs = Histogram cs (histMap cs xs)
+fill :: (Foldable f) => [Double] -> f Double -> Histogram
+fill cs xs = Histogram cs (foldl' (\x a -> Map.insertWith (+) (cutI cs a) 1 x) Map.empty xs)
+
+-- | find the index of the bucket the value is contained in.
+cutI :: (Ord a) => [a] -> a -> Int
+cutI bs n = go bs 0
   where
-    histMap cs' xs' =
-      L.fold count $
-        (\x -> L.fold countBool (fmap (x >) cs')) <$> xs'
-    count = L.premap (,1.0) countW
-    countBool = L.Fold (\x a -> x + if a then 1 else 0) 0 id
-    countW = L.Fold (\x (a, w) -> Map.insertWith (+) a w x) Map.empty id
+    go [] i = i
+    go (x:xs) i = bool i (go xs (i+1)) (n>x)
 
 -- | Make a histogram using n equally spaced cuts over the entire range of the data
 --
diff --git a/src/NumHask/Space/Time.hs b/src/NumHask/Space/Time.hs
--- a/src/NumHask/Space/Time.hs
+++ b/src/NumHask/Space/Time.hs
@@ -18,7 +18,6 @@
 import qualified Data.Text as Text
 import Data.Text (Text)
 import Data.Time
-import GHC.Base (String)
 import GHC.Generics
 import NumHask.Space.Types
 import Prelude
@@ -204,7 +203,7 @@
 -- | whether to include lower and upper times
 data PosDiscontinuous = PosInnerOnly | PosIncludeBoundaries
 
--- | dates attached to charts are often discontinuous, but we want to smooth that reality over and show a continuous range on the axis
+-- | dates used for time series analysis or attached to charts are often discontinuous, but we want to smooth that reality over and show a continuous range on the axis
 -- The assumption with getSensibleTimeGrid is that there is a list of discountinuous UTCTimes rather than a continuous range.  Output is a list of index points for the original [UTCTime] and label tuples, and a list of unused list elements.
 --
 -- >>> placedTimeLabelDiscontinuous PosIncludeBoundaries (Just "%d %b") 2 [UTCTime (fromGregorian 2017 12 6) 0, UTCTime (fromGregorian 2017 12 29) 0, UTCTime (fromGregorian 2018 1 31) 0, UTCTime (fromGregorian 2018 3 3) 0]
diff --git a/src/NumHask/Space/Types.hs b/src/NumHask/Space/Types.hs
--- a/src/NumHask/Space/Types.hs
+++ b/src/NumHask/Space/Types.hs
@@ -28,6 +28,7 @@
 where
 
 import Prelude
+import Data.Kind (Type)
 
 -- | Space is a continuous range of numbers that contains elements and has an upper and lower value.
 --
@@ -42,7 +43,7 @@
 class Space s where
 
   -- | the underlying element in the space
-  type Element s :: *
+  type Element s :: Type
 
   -- | lower boundary
   lower :: s -> Element s
@@ -162,7 +163,7 @@
 -- > getUnion (sconcat (Union <$> (gridSpace s g))) == s
 class (Space s, Num (Element s)) => FieldSpace s where
 
-  type Grid s :: *
+  type Grid s :: Type
 
   -- | create equally-spaced elements across a space
   grid :: Pos -> s -> Grid s -> [Element s]