[Haskell-beginners] Function for working with functions in data?

[Brandon S Allbery KF8NH]

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On 5/6/11 14:57 , Mike Meyer wrote:
> I'm filling a functional itch that Haskell isn't scratching. I'm
> looking for a function to take a list of functions, and apply them all
> to a value. The signature is obvious :: [a -> b] -> a -> [b], and it's
> nearly trivial to write (\fs a -> map ($ a) [fs]), but Haskell has
> most useful list functions already provided.

It's there, but it's not a dedicated function; it's "sequence" applied to
the environment monad (-> e).

    Prelude Control.Monad.Reader> :t sequence
    sequence :: (Monad m) => [m a] -> m [a]
    Prelude Control.Monad.Reader> :t sequence [(+1),(*2),(`subtract` 3)]
    sequence [(+1),(*2),(`subtract` 3)] :: (Num a) => a -> [a]

- -- 
brandon s. allbery     [linux,solaris,freebsd,perl]    allbery.b at gmail.com
system administrator  [openafs,heimdal,too many hats]                kf8nh
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