Darryn Reid wrote:
Martijn van Steenbergen wrote:
A small remark: I prefer using applicative notation for this:
go Next (Single x t1) = Single x <$> rewrite f t1 go Next (Fork t1 t2 ) = Fork <$> rewrite f t1 <*> rewrite f t2
Thanks for your comment and advice. Could you explain a little further your thinking? Specifically, what advantage do you find in the applicative notation, and when would you advise using it and when would you advise not using it?
The applicative notation is more general since it also applies to applicative functors http://www.cs.nott.ac.uk/~ctm/IdiomLite.pdf It's main advantage over the liftM family is that it can be used with any number of arguments liftM f m = f <$> m liftM2 f m n = f <$> m <*> n liftM3 f m n o = f <$> m <*> n <*> o etc. and that's why I prefer it as well. It's very similar to function application, too, just think of <*> as a replacement for the empty space that separates function arguments. The only drawback is probably that you have to import Control.Applicative In fact, it doesn't actually work for monads, I think you have to wrap it in a newtype. :D The same effect can be achieved with `ap` , though: liftM3 f m n p = return f `ap` m `ap` n `ap` o Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com