Jensen's Device: Difference between revisions

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@@ Line 809: / Line 809: @@
 import Data.STRef
-sum_ :: STRef s Double -> Double -> Double -> ST s Double -> ST s Double
+sum_ :: STRef s Double -> Double -> Double
+     -> ST s Double -> ST s Double
-sum_ ref_i lo hi term = sum <$> mapM ((>> term) . writeSTRef ref_i) [lo .. hi]
+sum_ ref lo hi term =
+   do
+     vs <- forM [lo .. hi]
+            (\k -> do { writeSTRef ref k
+                      ; term } )
+     return $ sum vs
 foo :: Double
 foo =
   runST $
-  do i <- newSTRef undefined -- initial value doesn't matter
+  do ref <- newSTRef undefined
-     sum_ i 1 100 $ recip <$> readSTRef i
+          -- initial value doesn't matter
+     sum_ ref 1 100 $
+       do
+         k <- readSTRef ref
+         return $ recip k
 main :: IO ()