Haskell: First parallel Haskell program

Haskell supports parallel and multi core programming. Following is an example of small parallel program application. I am not going to explain any details, just want to show how easy it is to develop parallel programs in Haskell. We can write parallel programs by using `par` expression.

Sample.hs

import Control.Parallel
 
main = a `par` b `par` c `pseq` print (a + b + c)
    where
        a = ackermann 3 10
        b = factorial 20
        c = fibonacci 20
 
factorial :: Integer -> Integer
factorial 0 = 1
factorial n = n * factorial (n-1)
 
ackermann :: Integer -> Integer -> Integer
ackermann m n
    | (m==0) = n+1
    | (m > 0) && (n==0) = ackermann (m-1) 1
    | (m > 0) && (n > 0) = ackermann (m-1) (ackermann m (n-1))

 
fibonacci :: Integer -> Integer
fibonacci 0 = 0
fibonacci 1 = 1
fibonacci n = fibonacci (n-1) + fibonacci (n-2)

Compiling with -threaded and optimisations on:

$ ghc -O2 --make Sample.hs -threaded -rtsopts
[1 of 1] Compiling Main             ( Sample.hs, Sample.o )
Linking Sample ...

Run multi core program using 2 cores.

$ time ./Sample +RTS -N2
2432902008176654954

real  0m1.309s
user  0m1.365s
sys 0m0.120s

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