On Sat, Nov 22, 2008 at 2:31 AM, Owen Smith
2. There's a lot I need to learn about good Haskell style, especially coming from a C++ background. Even my experience in Lisp seems to result in way more parentheses than Haskell coders are comfortable with. :-) In particular, I'm curious about how people actually use monadic operators. The following simple forms with the Maybe monad, for example, appear to be equivalent (hope I and QuickCheck are right about that!):
foo :: Int -> Maybe Int bar :: Int -> Maybe Int baz :: Int -> Maybe Int
baz n = (foo n) >>= bar baz n = bar =<< (foo n) baz n = (foo >=> bar) n baz n = (foo <=< bar) n
and I'm thinking the latter two are more idiomatically written as:
baz = foo >=> bar -- I think this one is my fave, naively speaking baz = bar <=< foo
You will find many differing opinions about this; just pick one that you find pretty and elegant. My personal style is never to use >>= or >=>; only =<< and <=<. These operators are for when I want monadic operations to feel like function application, which has the data flowing right to left. When I want monadic operations to feel like sequencing, I always use do notation. This is a particular case of my general inclination to have data in my progarm flow from top to bottom and right to left. (However I still often "read" it left to right; but I am inconsistent about that, and often switch back and forth when trying to comprehend a piece of code) Luke