Re: [Haskell-cafe] Using a monad to decompose a function into functions

14 Mar 2009


      On Friday 13 March 2009, Cristiano Paris wrote:
...
2009/3/13 Marcin Kosiba :
...
Hi,
       I've already checked those out. I tried using your yield
implementation and while it works, I couldn't get it to work with the
state monad.
       So while:
data RecPair a b = Nil | RP (b, a -> RecPair a b)
yield x = Cont $ \k -> RP (x, k)
       got me half-way to my goal, I couldn't figure out how to make
something like:
yield' = do
 state <- get
 state' <- yield state
 put state'
Basically, the yield is built upon the Cont monad which has a
transformer counter part, ContT. You could try and re-implement the
yield under ContT instead of just Cont then you can stack ContT on top
of State (or StateT if you need more monads) and have a state (i.e.
get/put) and the yield.
Great! That helped a lot. I'm attaching a ConT yield implementation and 
another one which also handles a return statement with a different type. Hope 
someone finds them useful.
	
Thanks!
	Marcin Kosiba