Editing GHC/Data Parallel Haskell/GHC.PArr (section)

== Convenience without the speed: syntactic sugar for a high-level array library ==

The following explains how to install and use parallel arrays and array comprehensions to prototype nested data-parallel algorithms in Haskell.

But your programs will only run sequentially!  That's what we mean by "convenience without speed"!

=== Installation ===

Any compiler in GHC's 6.8 series includes support for parallel arrays.  It is invoked by supplying the compiler option <tt>-XPArr</tt> and importing the module <hask>GHC.PArr</hask>.  Moreover, to use [http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#parallel-list-comprehensions parallel array comprehensions], the compiler option <tt>-fglasgow-exts</tt> is required.  

'''Caveat:''' This version of DPH is essentially an initial high-level prototype that we '''do not support''' anymore.  Feel free to use it to experiment with the array syntax, but please do not expect good performance.

=== A small example ===

The following module implements the dot product of two vectors using parallel arrays:

<haskell>
{-# OPTIONS -fparr -fglasgow-exts #-}
module DotP (dotp)
where
import GHC.PArr

dotp :: Num a => [:a:] -> [:a:] -> a
dotp xs ys = sumP [:x * y | x <- xs | y <- ys:]
</haskell>

You can use this module in an interactive GHCi session as follows:

<blockquote><pre>
Prelude> :set -fparr -fglasgow-exts
Prelude> :load DotP
[1 of 1] Compiling DotP             ( code/haskell/DotP.hs, interpreted )
Ok, modules loaded: DotP.
*DotP> dotp [:1..3:] [:4..6:]
32
*DotP>
</pre></blockquote>
(NB: The <tt>:set</tt> is needed despite the <tt>OPTIONS</tt> pragma in <tt>DotP.hs</tt>, so that you can use array syntax on the interactive command line of GHCi.)

Unfortunately, the current version of Haddock does not grok the special array syntax, so there is no nice HTML version of the interface of <hask>GHC.PArr</hask>.  Instead, please consult the [http://darcs.haskell.org/packages/base/GHC/PArr.hs source code of <hask>GHC.PArr</hask>] for details on the supplied array operations.