Re: Replaced throw to throwIO where type is IO

25 Sep 2010

      On Sat, Sep 25, 2010 at 4:41 PM, Bas van Dijk  wrote:
...
However I do wonder why onException is using throw instead of the
recommended throwIO. Has this to do with performance since they're
both primitive operations:
throw :: Exception e => e -> a
throw e = raise# (toException e)
throwIO :: Exception e => e -> IO a
throwIO e = IO (raiseIO# (toException e))
I think I found the answer myself.

I see that raiseIO# is implemented as jumping to the implementation of raise#:

rts/Exception.cmm line: 588

stg_raiseIOzh
{
  /* Args :: R1 :: Exception */
  jump stg_raisezh;
}

So I guess using #raise directly is faster since it doesn't need to
perform the jump.

I'll see if I can make some Criterion benchmarks to see if it's actually faster.

Bas