Re: [Haskell-cafe] Seeking help to generalize this ..

Related: In Data.Monoid there is the 'Endo' newtype, which wraps functions of type 'a -> a'. Is there an 'EndoM' variant, or is that something that's usually created by putting other pieces together? Below is a sketch of what I mean: -- Maybe this is known by another name? newtype EndoM f a = EndoM { appEndoM :: a -> f a } -- Bind typeclass is from package semigroupoids. -- It means "Monad sans 'return'". -- Maybe use Monad f => here instead if getting the Bind instances is -- too annoying? (e.g., Writing orphan instances). instance Bind f => Semigroup (EndoM f a) where EndoM f <> EndoM g = EndoM $ f ->- g -- Bind is not a superclass of Monad, so we get this awkward set of -- required constraints here. instance (Bind f, Monad f) => Monoid (EndoM f a) where mempty = EndoM pure -- Jack Justin Paston-Cooper writes:

Hello,

I suggest taking a quick look at the function ‘fold’ in Data.Foldable, and also Data.Functor.Compose. That should be good start for composing any list of such functions.

Cheers,

J.

On Sat, 1 Feb 2020 at 19:55, Debasish Ghosh wrote:

...

Hi -

How can I generalize the following pattern to an arbitrary list of functions ?

compose :: (Monad m) => (Foo -> m Foo) -> (Foo -> m Foo) -> (Foo -> m Foo) -> Foo -> m Foo compose f1 f2 f3 acc = do a <- f1 acc b <- f2 a f3 b

Any help please .. regards.

-- Debasish Ghosh http://manning.com/ghosh2 http://manning.com/ghosh

Twttr: @debasishg Blog: http://debasishg.blogspot.com Code: http://github.com/debasishg _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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