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
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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