On Thu, Mar 31, 2011 at 11:01 AM, Matthew Steele
On Mar 30, 2011, at 5:29 PM, Mathijs Kwik wrote:
So loop really doesn't seem to help here, but I couldn't find another way either to feed outputs back into the system. What I need is: Either A B ~> Either C B -> A ~> C
Does such a thing exist?
Based on your description, it sounds to me like you want a loop such that if a B is generated at the end, you send it back to the start and execute your arrow a second time. Is that in fact what you intended? However, the docs for ArrowLoop's loop function make it clear that it executes the arrow only once:
http://www.haskell.org/ghc/docs/latest/html/libraries/base-4.3.1.0/Control-A...
If your arrows are instances of ArrowApply, I believe you could use app to implement the combinator you want.
If your arrow's combinators are lazy enough, you can do something like this:
foo :: ArrowChoice (~>) => (Either a b ~> Either c b) -> (a ~> c)
foo f = (id ||| bar) . f . arr Left
where
bar = (id ||| bar) . f . arr Right
But maybe Arrow isn't the proper abstraction. Perhaps something more
similar to Fudgets is appropriate?
--
Dave Menendez