Anish Muttreja ha scritto:
On Sun, Mar 01, 2009 at 07:25:56PM +0100, Manlio Perillo wrote:
Hi.
I have a function that do some IO (take a file path, read the file,
parse, and return some data), and I would like to parallelize it, so
that multiple files can be parsed in parallel.
I would like to use the simple mapReduce function,
from Real Word Haskell:
mapReduce :: Strategy b -- evaluation strategy for mapping
-> (a -> b) -- map function
-> Strategy c -- evaluation strategy for reduction
-> ([b] -> c) -- reduce function
-> [a] -- list to map over
-> c
mapReduce mapStrat mapFunc reduceStrat reduceFunc input =
mapResult `pseq` reduceResult
where mapResult = parMap mapStrat mapFunc input
reduceResult = reduceFunc mapResult `using` reduceStrat
Is this possible?
Thanks Manlio Perillo
Would this work?
I suspect that it will not work..
Read in each file into a string (or byteString) using a lazy function
and then call mapReduce with the strings instead of file paths.
import qualified Data.Bytestring.Lazy.Char8 as L
do
let handles = map (openFile ) files
strings <- mapM L.hGetContents handles
let result = mapReduce ...
The actual work of reading in the file should happen on-demand inside the
parsing function called by mapReduce.
By doing this I will probably lose any control about file resources usage.
Thanks Manlio
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