Hi, If I have this Foo.hs: ------------------------------- module Foo (foo) where import Word (Word8) import Control.Monad.ST (ST) import Data.Array.ST (STUArray, writeArray) foo :: STUArray s Int Word8 -> [Word8] -> Int -> ST s () foo arr ps i = writeArray arr i w where i' = 4 * i w = ps !! i' ------------------------------- and I compile with (GHC 6.2 and a reasonably recent CVS) ghc -O -funbox-strict-fields -Wall -c Foo.hs -ddump-simpl then part of the output is: let { n :: GHC.Prim.Int# Str: DmdType n = GHC.Prim.*# 4 ww3 } in case GHC.Prim.<# n 0 of wild1 { Is this really a lazy let, or is there some magic going on that means it is actually done strictly as it's an Int#? Like how ISTR Int#s always appear to have strictness L (these inconsitencies make things much more difficult as a user IMO, incidentally). Thanks Ian