On Wed, Nov 28, 2018 at 09:39:01AM -0800, Ryan Reich wrote:
Thanks for the suggestion, which Arjen made also. Unfortunately, it does not appear to help. See this simple program:
-- Loop.hs import Control.Exception import System.Timeout
main :: IO (Maybe Integer) main = timeout 100000 $ evaluate $ last $ repeat 0 -- end
With either GHC invocation "stack exec ghc Loop[ -- -fno-omit-yields]", running ./Loop fails to terminate (it should do so in 0.1s).
Based only on the very terse description of that flag in the User's Guide, and its name, I think the problem is simply that GHC doesn't normally *generate* yields in that loop, so there's nothing not to omit.
It times out for me with GHC 8.4.4 on FreeBSD 11.2, and "ghc -O -fno-omit-yields" and does not time out with "ghc -O": $ cat /tmp/foo.hs import Control.Exception import System.Timeout main :: IO (Maybe Integer) main = timeout 1000000 $ evaluate $ last $ repeat 0 $ ghc -O -fno-omit-yields /tmp/foo.hs [1 of 1] Compiling Main ( /tmp/foo.hs, /tmp/foo.o ) [Optimisation flags changed] Linking /tmp/foo ... $ time /tmp/foo real 0m1.033s user 0m1.025s sys 0m0.008s $ rm /tmp/foo $ ghc -O /tmp/foo.hs [1 of 1] Compiling Main ( /tmp/foo.hs, /tmp/foo.o ) [Optimisation flags changed] Linking /tmp/foo ... $ time /tmp/foo ^C^C real 0m5.864s user 0m5.857s sys 0m0.000s On MacOS X with GHC 7.10.3, it does not time out either way. Perhaps some versions of GHC don't make the timeout possible. -- Viktor.