Thanks Brent, I think I understood your point: In my form a ->> f ->> g, there are parentheses like (a ->> f) ->> g, and the parenth expression resolves to a value, whereas in a >$> f >>> g, there are parentheses like a >$> (f >>> g), and the parenth expression is a function which is much more flexible. Tim 2010/11/20 Brent Yorgey :

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 _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners