Update cabal + add wrapper over MWC

Statistics/Distribution/Poisson.hs

@@ -31,18 +31,24 @@
 import Data.Binary          (Binary(..))
 import Data.Data            (Data, Typeable)
 import GHC.Generics         (Generic)
+
+import qualified System.Random.MWC.Distributions as MWC
+
 import Numeric.SpecFunctions (incompleteGamma,logFactorial)
 import Numeric.MathFunctions.Constants (m_neg_inf)
 
+
 import qualified Statistics.Distribution as D
 import qualified Statistics.Distribution.Poisson.Internal as I
 import Statistics.Internal
+import Control.Monad (liftM)
+
 
 
 
 newtype PoissonDistribution = PD {
       poissonLambda :: Double
     } deriving (Eq, Typeable, Data, Generic)
 
 instance Show PoissonDistribution where
   showsPrec i (PD l) = defaultShow1 "poisson" l i
@@ -93,6 +99,12 @@
 instance D.MaybeEntropy PoissonDistribution where
   maybeEntropy = Just . D.entropy
 
+instance D.DiscreteGen PoissonDistribution where
+  genDiscreteVar (PD lambda) = MWC.poisson lambda
+
+instance D.ContGen PoissonDistribution where
+  genContVar (PD lambda) gen = fromIntegral <$> MWC.poisson lambda gen
+
 -- | Create Poisson distribution.
 poisson :: Double -> PoissonDistribution
 poisson l = maybe (error $ errMsg l) id $ poissonE l

statistics.cabal

@@ -128,7 +128,7 @@ library
   build-depends: base                    >= 4.9 && < 5
                  --
                , math-functions          >= 0.3.4.1
-               , mwc-random              >= 0.15.0.0
+               , mwc-random              >= 0.15.3.0
                , random                  >= 1.2
                  --
                , aeson                   >= 0.6.0.0