What does . (dot) stands in haskell?

What does . (dot) stands in haskell?

>Solution :

The . stands for function composition in Haskell.

It allows you to chain different functions. In your case, instead of doing a new function that calls toDigits and then sum over the result, you can use function composition.

sumDigits = sum (map myFunction)

myFunction xs = sum (toDigits xs)

The definition of . is the following.

(.) :: (b -> c) -> (a -> b) -> a -> c  
f . g = \x -> f (g x) 

There’s a really good example on stackoverflow already you can check.

Say you have these functions:

even :: Int -> Bool
not :: Bool -> Bool

and you want to define your own myOdd :: Int -> Bool function using
the two above.

The obvious way to do this is the following:

myOdd :: Int -> Bool myOdd x = not (even x)

But this can be done more succinctly using function composition:

myOdd :: Int -> Bool myOdd = not . even

The myOdd functions behave exactly the same, but the second one is
created by "glue-ing" two functions together.