[Haskell-beginners] parallel program in haskell in 5 steps

[Michael Snoyman]

How are you running the program? You have to explicitly tell the
compiler/interpreter to use multiple system threads.

Michael

On Tue, May 5, 2009 at 10:19 PM, Jack Kennedy <jack at realmode.com> wrote:

> In step 4 of Haskell in 5 Steps [
> http://haskell.org/haskellwiki/Haskell_in_5_steps],
> a parallel program is given. I changed it very slightly so it would run a
> long time (see below).
>
> It compiles and runs but my CPU meter is barely above 50%.  I have a dual
> core processor.
> What in the world would keep this program from completely saturating the
> CPU?
>
> import Control.Parallel
>
> main = a `par` b `pseq` print (a + b)
>     where
>         a = ack 4 10
>         b = ack 4 10
>
> fac 0 = 1
> fac n = n * fac (n-1)
>
> ack 0 n = n+1
> ack m 0 = ack (m-1) 1
> ack m n = ack (m-1) (ack m (n-1))
>
> fib 0 = 0
> fib 1 = 1
> fib n = fib (n-1) + fib (n-2)
>
>
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