I was playing around a little more and I noticed that stack sets the following ghc-options by default: -threaded -rtsopts -with-rtsopts=-N which I assumed

I was playing around a little more and I noticed that stack sets the following ghc-options by default: -threaded -rtsopts -with-rtsopts=-N which I assumed explained some of the speedup, so I disabled them and got a reduction to 99% cpu as expected, but unexpectedly the single threaded version was about twice as fast: % make hs Results: [24605537,25150983,21576960] make hs 3.13s user 0.07s system 99% cpu 3.211 total