Dusan Kolar wrote: > Hello all, > > the following program changes behavior if translated using different > options for ghc compiler. Is this correct or not? I used The Glorious > Glasgow Haskell Compilation System, version 6.6. And I would expect in > both cases behavior 1. > > But I may be wrong...
You do not get to expect that unsafe* function are unaffected by optimizations. > > Thanks for any resolution. > > Dusan > > > *Program:* > > $ cat Test.hs > import System.IO.Unsafe > import System.IO > > main = do > putStr "Start...\n" > putStr $ show $ falling' falling10000 > putStr "\n" > putStr $ show $ sorted' rising10000 > putStr "Stop...\n" > > sorted' [] = True > sorted' [_] = True > sorted' l = sx l 1 > where > sx [] _ = True > sx [_] _ = True > sx (x:l@(y:ys)) n = > if n==1000 then unsafePerformIO (putChar '.' >> hFlush stdout) > `seq` x<=y && sx l 1 > else x<=y && (sx l $! n+1) > > falling' [] = True > falling' [_] = True > falling' l = sx l 1 > where > sx [] _ = True > sx [_] _ = True > sx (x:l@(y:ys)) n = > if n==1000 then unsafePerformIO (putChar '.' >> hFlush stdout) > `seq` x>=y && sx l 1 > else x>=y && (sx l $! n+1) > > rising10000 = [0..100000] > > falling10000 = [100000,99999..0] > > -- EOF > the expression > unsafePerformIO (putChar '.' >> hFlush stdout) has type "()" and does not depend on anything in scope. The `seq` command demands that this be evaluated to see it is bottom or the value "()", but then it never needs to be re-evaluated, as Haskell may assume it is will be immutably the value "()". > > > *Behavior 1:* > > $ ghc Test.hs -o test > $ ./test > Start... > ....................................................................................................True > > ....................................................................................................TrueStop... There it is re-evaluated. > > > > *Behavior 2:* > > $ rm test Test.o Test.hi > $ ghc -O2 Test.hs -o test > $ ./test > Start... > .True > .TrueStop... > There it is evaluated once and cached. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
