Am Dienstag 15 Dezember 2009 21:50:22 schrieb Johann Höchtl:
It's b, compiled without optimisations.
Don't do that. Maybe if you have huge projects with large compile times. But without optimisations, small variations can incur huge performance costs (as we see here).
If a) or b), it's because the second has one more function call per list element, first ($!) is called and then seq via that, while the first calls seq directly.
Ah, ok, I was not aware that this is realy a function call. I thought this is syntactic sugar only and would be rewritten into a call to `seq`. I think to much of a macro in this case.
It's a real function, defined in Haskell. Unfortunately, without -O, ghc is not keen to inline across module boundaries. It would be inlined within the same module. seq is a primitive from GHC.prim, thus it's special and doesn't produce a function call.