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Manfred Lotz

20 Aug 2011 20 Aug '11

1:42 p.m.

Hi all, Maybe a stupid question. I have a list of functions [IO ()] and want to run those functions one after another. I did this runList :: [IO ()] -> IO () runList [] = return () runList (f:fs) = do f runList fs which works fine. However, I'm curious if there is a library function doing exactly this? -- Manfred

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David Place

20 Aug 20 Aug

2:08 p.m.

sequence_ :: Monad m => [m a] -> m () ____________________ David Place Owner, Panpipes Ho! LLC http://panpipesho.com d@vidplace.com On Aug 20, 2011, at 1:42 PM, Manfred Lotz wrote:

Hi all, Maybe a stupid question.

I have a list of functions [IO ()] and want to run those functions one after another.

I did this

runList :: [IO ()] -> IO () runList [] = return () runList (f:fs) = do f runList fs

which works fine.

However, I'm curious if there is a library function doing exactly this?

-- Manfred

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

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Manfred Lotz

2:36 p.m.

On Sat, 20 Aug 2011 14:08:43 -0400 David Place wrote:

sequence_ :: Monad m => [m a] -> m ()

Thanks. I found sequence but I have to learn to add an underscore to a funtion in order to see if this could be it. -- Manfred

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Ozgur Akgun

3:21 p.m.

Hi. On 20 August 2011 19:36, Manfred Lotz wrote:

On Sat, 20 Aug 2011 14:08:43 -0400 David Place wrote:

...
sequence_ :: Monad m => [m a] -> m ()

Thanks. I found sequence but I have to learn to add an underscore to a funtion in order to see if this could be it.

Actually in this case sequence and sequence_ are identical. You have IO for m, and () for a, so: sequence :: [IO ()] -> IO () sequence_ :: [IO ()] -> IO () Ozgur

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Brandon Allbery

3:31 p.m.

On Sat, Aug 20, 2011 at 15:21, Ozgur Akgun wrote:

sequence :: [IO ()] -> IO () sequence_ :: [IO ()] -> IO ()

sequence isn't ([IO ()] -> IO [()])? -- brandon s allbery allbery.b@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms

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Ozgur Akgun

3:50 p.m.

I stand corrected. Sorry for the additional confusion. On 20 August 2011 20:31, Brandon Allbery wrote:

On Sat, Aug 20, 2011 at 15:21, Ozgur Akgun wrote:

...
sequence :: [IO ()] -> IO () sequence_ :: [IO ()] -> IO ()

sequence isn't ([IO ()] -> IO [()])?

-- Ozgur Akgun

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Ertugrul Soeylemez

3:35 p.m.

Ozgur Akgun wrote:

Actually in this case sequence and sequence_ are identical. You have IO for m, and () for a, so:

sequence :: [IO ()] -> IO () sequence_ :: [IO ()] -> IO ()

No, compare the type signatures: sequence :: [IO ()] -> IO [()] sequence_ :: [IO ()] -> IO () In the former case you will receive a list of as many values of type () as there are actions. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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participants (5)

Brandon Allbery
David Place
Ertugrul Soeylemez
Manfred Lotz
Ozgur Akgun