Maybe this is an often asked question, but I did not found an answer.
The bind of a monad is defined like that:
(>>=) :: m a -> (a -> m b) -> m b
At the moment I'm doing this:
foo :: Int
foo = sum $ ((*11) . (+2)) `map` [1..4]
I want to achieve a syntax like this, because I think it's more readable:
[1..4] >>= (+2) >>= (*11) >>= sum
I don't know the right operators instead of >>=
.
Besides: foo is 198.
The most readable in this case is certainly
sum [ (x+2)*11 | x<-[1..4] ]
but if you want it point-free and without extra parens, just rewrite your original line with the infix fmap operator :
sum $ (*11) . (+2) <$> [1..4]
If you just want to turn the order around, you can replace .
with the equivalent flipped operator from Control.Category
, and $
with its flipped version eg from lens
[1..4] & fmap((+2)>>>(*11)) & sum
Then again, if you're after mathematical elegance and want it to "work like a monad", this isn't possible because there's nothing monadic going on here. You could however argue that sum
is a Cokleisli arrow in the (not definable, in Haskell 98) Monoid
-limited list comonad. We can approximate this by the NonEmpty comonad and write
extract $ fromList [1..4] =>> (extract>>>(+2)>>>(*11)) =>> sum.toList
but this is ridiculous.
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