diff --git a/positive.cabal b/positive.cabal
--- a/positive.cabal
+++ b/positive.cabal
@@ -1,12 +1,12 @@
 
 name:               positive
-version:            0.3
+version:            0.4
 cabal-version:      >= 1.10
 author:             Hans Hoglund
 maintainer:         Hans Hoglund <hans@hanshoglund.se>
 license:            BSD3
 license-file:       COPYING
-synopsis:           Positive numbers.
+synopsis:           Positive integers.
 category:           
 tested-with:        GHC
 build-type:         Simple
@@ -21,7 +21,8 @@
 library
     build-depends:
         base            >= 4 && < 5,
-        nats            >= 0.2 && < 1
+        nats            >= 0.2 && < 1,
+        semigroups      >= 0.15.2 && < 1
     hs-source-dirs:     src
     default-language:   Haskell2010
     exposed-modules:
diff --git a/src/Numeric/Positive.hs b/src/Numeric/Positive.hs
--- a/src/Numeric/Positive.hs
+++ b/src/Numeric/Positive.hs
@@ -3,9 +3,13 @@
 
 module Numeric.Positive (
         Positive,
-        positive
+        positive,
+        nonEmptyLength,
   ) where
+
 import Numeric.Natural
+import Data.Semigroup
+import qualified Data.List.NonEmpty as NonEmpty
 
 newtype Positive = Positive { getPositive :: Natural } deriving
     ( 
@@ -54,3 +58,13 @@
 positive :: a -> (a -> a) -> Positive -> a
 positive a f 1 = f a
 positive a f n = f (positive a f $ pred n)
+
+nonEmptyLength :: NonEmpty.NonEmpty a -> Positive
+nonEmptyLength = fromIntegral . NonEmpty.length
+
+-- _positive :: Integral a => Prism' a Positive
+-- _positive :: prism' fromIntegral (\x -> if x > 0 then Just (fromInteger x :: Positive) else Nothing)
+
+-- _nonEmpty :: Prism [a] [b] (NonEmpty a) (NonEmpty b)
+-- _nonEmpty :: prism' NonEmpty.toList (\x -> if lenght x > 0 then Just (NonEmpty.fromList x) else Nothing)
+