8c6794b6.github.io

In haddock of dph-par package, we see functions like below:

zipP :: [:a:] -> [:b:] -> [:(a, b):]
{-# NOINLINE zipP #-}
zipP !_ !_ = [::]
{-# VECTORISE zipP = zipPA #-}

Above difinition is from dph-par-0.5.1.1. From what its written, zipP looks like a function that returning an empty array. Though after compiling the code with appropriate options, zipP indeed work as parallel variant of zip for standard list.

As of GHC-7.2.2 and dph-par-0.5.1.1, we cannot directly load codes with parallel array in ghci. One way to load them in ghci is, prepare a wrapper with fixing the type of array element, and compile to object code.

Suppose that we have a module containing parallel array functions:

{-# LANGUAGE ParallelArrays #-}
{-# OPTIONS_GHC -fvectorise #-}
-- VectroseMe.hs
module VectoriseMe where

import Data.Array.Parallel
import Data.Array.Parallel.PArray

myZipP :: [:a:] -> [:b:] -> [:(a, b):]
myZipP as bs = zipP as bs

myZipPA :: PArray a -> PArray b -> PArray (a, b)
myZipPA as bs = toPArrayP (myZipP (fromPArrayP as) (fromPArrayP bs))
{-# NOINLINE myZipPA #-}

myZipIntP :: [:Int:] -> [:Int:] -> [:(Int, Int):]
myZipIntP as bs = zipP as bs

myZipIntPA :: PArray Int -> PArray Int -> PArray (Int, Int)
myZipIntPA as bs = toPArrayP (myZipIntP (fromPArrayP as) (fromPArrayP bs))
{-# NOINLINE myZipIntPA #-}

And a wrapper which imports above module:

-- Wrapper.hs
module Wrapper where

import Data.Array.Parallel
import Data.Array.Parallel.PArray (fromList)

import VectoriseMe

main :: IO ()
main = do
  putStrLn $ concat ["myZip_test:", "\n  ", show myZip_test]
  putStrLn $ concat ["myZipInt_test:", "\n  ", show myZipInt_test]

pa1, pa2 :: PArray Int
pa1 = fromList [1,2,3]
pa2 = fromList [4,5,6]

myZip_test :: PArray (Int, Int)
myZip_test = myZipPA pa1 pa2

myZipInt_test :: PArray (Int, Int)
myZipInt_test = myZipIntPA pa1 pa2

Loading Wrapper.hs in ghci and invoking the main function:

| $ ghci -fdph-par -fobject-code -fforce-recomp Wrapper.hs
| GHCi, version 7.2.2: http://www.haskell.org/ghc/  :? for help
| Loading package ghc-prim ... linking ... done.
| Loading package integer-gmp ... linking ... done.
| Loading package base ... linking ... done.
| Loading package array-0.3.0.3 ... linking ... done.
| Loading package old-locale-1.0.0.3 ... linking ... done.
| Loading package time-1.2.0.5 ... linking ... done.
| Loading package random-1.0.1.1 ... linking ... done.
| Loading package primitive-0.3.1 ... linking ... done.
| Loading package vector-0.7.1 ... linking ... done.
| Loading package dph-base-0.5.1.1 ... linking ... done.
| Loading package dph-prim-interface-0.5.1.1 ... linking ... done.
| Loading package dph-prim-seq-0.5.1.1 ... linking ... done.
| Loading package old-time-1.0.0.7 ... linking ... done.
| Loading package dph-prim-par-0.5.1.1 ... linking ... done.
| Loading package containers-0.4.1.0 ... linking ... done.
| Loading package filepath-1.2.0.1 ... linking ... done.
| Loading package unix-2.5.0.0 ... linking ... done.
| Loading package directory-1.1.0.1 ... linking ... done.
| Loading package pretty-1.1.0.0 ... linking ... done.
| Loading package process-1.1.0.0 ... linking ... done.
| Loading package Cabal-1.12.0 ... linking ... done.
| Loading package bytestring-0.9.2.0 ... linking ... done.
| Loading package binary-0.5.0.2 ... linking ... done.
| Loading package bin-package-db-0.0.0.0 ... linking ... done.
| Loading package hoopl-3.8.7.1 ... linking ... done.
| Loading package hpc-0.5.1.0 ... linking ... done.
| Loading package template-haskell ... linking ... done.
| Loading package ghc-7.2.2 ... linking ... done.
| Loading package dph-par ... linking ... done.
| Loading package ffi-1.0 ... linking ... done.
| [1 of 2] Compiling VectoriseMe      ( VectoriseMe.hs, VectoriseMe.o )
| [2 of 2] Compiling Wrapper          ( Wrapper.hs, Wrapper.o )
| Ok, modules loaded: Wrapper, VectoriseMe.
| ghci> main
| myZip_test:
|   fromList<PArray> []
| myZipInt_test:
|   fromList<PArray> [(1,4),(2,5),(3,6)]

We see that myZip_test is showing empty list, and myZipInt_test is showing the zipped contents.