diff --git a/mcmc-synthesis.cabal b/mcmc-synthesis.cabal
--- a/mcmc-synthesis.cabal
+++ b/mcmc-synthesis.cabal
@@ -10,7 +10,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.1.0.5
+version:             0.1.1.0
 
 -- A short (one-line) description of the package.
 synopsis:            MCMC applied to probabilistic program synthesis
diff --git a/src/Language/Synthesis/Distribution.hs b/src/Language/Synthesis/Distribution.hs
--- a/src/Language/Synthesis/Distribution.hs
+++ b/src/Language/Synthesis/Distribution.hs
@@ -1,7 +1,7 @@
 {-# LANGUAGE RankNTypes #-}
 module Language.Synthesis.Distribution (
     Distr (Distr), sample, logProbability, negativeInfinity, sumByLogs,
-    categorical, uniform, randInt, replicate, mix
+    categorical, uniform, randInt, replicate, mix, constant
 ) where
 
 import           Prelude              hiding (replicate)
@@ -21,6 +21,12 @@
 -- |Negative infinity, the log of 0 probability.
 negativeInfinity :: Double
 negativeInfinity = read "-Infinity"
+
+
+-- |A distribution containing a single item.
+constant :: a -> Distr a
+constant item = Distr { sample = return item
+                      , logProbability = const 0 }
 
 -- |Computes (log . sum . map exp), with more numeric precision.
 sumByLogs :: [Double] -> Double