X-Git-Url: https://mattmccutchen.net/match/match.git/blobdiff_plain/e42ffb752c2f93342a84239b552ca062afffefd3..35ce78e3b164a71da6177f0577b598a12198d237:/program/RandomizedMonad.hs

diff --git a/program/RandomizedMonad.hs b/program/RandomizedMonad.hs
index 62e8808..22b98aa 100644
--- a/program/RandomizedMonad.hs
+++ b/program/RandomizedMonad.hs
@@ -3,7 +3,7 @@ module RandomizedMonad (
 	msplit,
 	runRandom1, runRandom, runRandomStd, runRandomNewStd,
 	mrandomR, mrandom,
-	withProb,
+	withProb, withWeight,
 	filterRandomized,
 	indReplicateRandom, indRepeatRandom, indRandomArray
 ) where
@@ -70,6 +70,13 @@ withProb ifCs elseR = do
 	val <- mrandom
 	chooseCase val ifCs elseR
 
+-- Like withProb, but without an else case and with the "probabilities" scaled
+-- so that they sum to 1.
+withWeight :: [(Double, Randomized a)] -> Randomized a
+withWeight ifCs = do
+	val <- mrandomR (0, sum (map fst ifCs))
+	chooseCase val (tail ifCs) (snd (head ifCs))
+
 -- Keep trying until we get what we want.
 filterRandomized :: (a -> Bool) -> Randomized a -> Randomized a
 filterRandomized f ra = do