On Sat, Nov 20, 2010 at 06:10:22PM +0100, Tim Baumgartner wrote:
Hi,
I really like fooling around with operators. In elementary school, we always had to make chain computations, e.g.
teacher: 2 teacher: +1 teacher: *2 teacher: divided by 3
Again, I didn't find the following operator on hoogle (very similar to ($)): (->>) :: a -> (a -> b) -> b a ->> f = f a
You can define (->>) as flip ($).
Using it, we can nicely write down the above computation: 2 ->> (+1) ->> (*2) ->> (`div` 3)
Another way to write this is using (>>>) from Control.Category which is essentially flipped function composition. Occasionally I will write things in this style and define (>$>) to be the same as your (->>), and write things like 2 >$> (+1) >>> (*2) >>> (`div` 3) If we did the same thing in right-to-left style, your code would correspond to (`div` 3) $ (*2) $ (+1) $ 2 whereas mine corresponds to (`div` 3) . (*2) . (+1) $ 2 The latter is generally considered better style, since any subsection of the "pipeline" on the left side of the $ is valid on its own, making it much easier to refactor (pull out pieces of the pipeline that are also used elsewhere and give them a name, and so on). Also, this form makes it clear that the 2 at the end is different. Simply removing the $ 2 gives a valid function that abstracts away from the specific starting value and will work for any starting value. -Brent