Haskell composition (.) vs F#'s pipe forward operator (|>)

Question

In F#, use of the the pipe-forward operator, |>, is pretty common. However, in Haskell I\'ve only ever seen function composition, (.), being us

Answer 1

Left-to-right composition in Haskell

Some people use left-to-right (message-passing) style in Haskell too. See, for example, mps library on Hackage. An example:

euler_1 = ( [3,6..999] ++ [5,10..999] ).unique.sum

I think this style looks nice in some situations, but it's harder to read (one needs to know the library and all its operators, the redefined (.) is disturbing too).

There are also left-to-right as well as right-to-left composition operators in Control.Category, part of the base package. Compare >>> and <<< respectively:

ghci> :m + Control.Category
ghci> let f = (+2) ; g = (*3) in map ($1) [f >>> g, f <<< g]
[9,5]

There is a good reason to prefer left-to-right composition sometimes: evaluation order follows reading order.