Re: [Haskell-cafe] List of functions

2 Sep 2005

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On 8/31/05, Krasimir Angelov  wrote:
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2005/8/31, Sebastian Sylvan :
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On 8/31/05, Dinh Tien Tuan Anh  wrote:
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Something like (untested)...
xs <- zipWith ($) forkIO (map (\f -> f x y) funs)
tids <- sequence xs
what does "zipWith ($)" do ?
$ is function application, so zipWith ($) will "zip" a list of
functions with a list of arguments, by applying the functions to
Mark Goldman writes:

the
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arguments pair-wise, producing a list of results.
But forkIO is function not a list of functions. The above example is
incorrect. I think it should be:
tids <- sequence [forkIO (f x y) | f <- funs]
The following corrects the zipWith example:
xs <- zipWith ($) (repeat forkIO) (map (\f -> f x y) funs)
tids <- sequence xs
It's not always obvious when to use sequence or mapM, but I think this
one calls for the latter.

    mapM (\f -> forkIO (f x y)) funs :: IO [ThreadId]

If you don't care about the thread IDs, then this is more efficient:

    mapM_ (\f -> forkIO (f x y)) funs :: IO ()
-- 
David Menendez  http://www.eyrie.org/~zednenem/