From 2c8d42f32022f4950606d75d53e45a4c30d210df Mon Sep 17 00:00:00 2001 From: "dias@eecs.tufts.edu" Date: Wed, 18 Mar 2009 21:01:38 +0000 Subject: [PATCH] Comment explaining use of seq in DFMonad --- compiler/cmm/DFMonad.hs | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/compiler/cmm/DFMonad.hs b/compiler/cmm/DFMonad.hs index 0cf1ead..263d0d4 100644 --- a/compiler/cmm/DFMonad.hs +++ b/compiler/cmm/DFMonad.hs @@ -192,6 +192,10 @@ instance Monad m => Monad (DFM' m f) where DFM' f >>= k = DFM' (\l s -> do (a, s') <- f l s s' `seq` case k a of DFM' f' -> f' l s') return a = DFM' (\_ s -> return (a, s)) + -- The `seq` is essential to ensure that entire passes of the dataflow engine + -- aren't postponed in a thunk. By making the sequence strict in the state, + -- we ensure that each action in the monad is executed immediately, preventing + -- stack overflows that previously occurred when finally forcing the old state thunks. instance FuelUsingMonad (DFM' FuelMonad f) where fuelRemaining = liftToDFM' fuelRemaining -- 1.7.10.4