Editing GHC/Data Parallel Haskell (section)

==== Using vectorised code ====

Finally, we need a main module that calls the vectorised code, but is itself not vectorised, so that it may contain I/O.  In this simple example, we convert two simple lists to parallel arrays, compute their dot product, and print the result:
<haskell>
import Data.Array.Parallel
import Data.Array.Parallel.PArray (PArray, fromList)

import DotP (dotp_wrapper)  -- import vectorised code

main :: IO ()
main
  = let v      = fromList [1..10]    -- convert lists...
        w      = fromList [1,2..20]  -- ...to parallel arrays
        result = dotp_wrapper v w    -- invoke vectorised code
    in
    print result                     -- print the result
</haskell>
We compile this module with
<blockquote>
<code>ghc -c -Odph -fdph-par Main.hs</code>
</blockquote>
and finally link the two modules into an executable <code>dotp</code> with
<blockquote>
<code>ghc -o dotp -threaded -fdph-par -rtsopts DotP.o Main.o</code>
</blockquote>
We need the <code>-threaded</code> option to link with GHC's multi-threaded runtime and <code>-fdph-par</code> to link with the standard parallel DPH backend.  We include <code>-rtsopts</code> to be able to explicitly determine the number of OS threads used to execute our code.