Hello,
Thank everybody for the answers.
I must admit that I did not really emphasize the goal behind my initial
question. Which is better expressed this way:
'walk' is written is CPS and is tail recursive. Unless I am wrong , if the
continuation monad is used, the recursive calls to 'walk' are
Excerpts from wren ng thornton's message of Thu Nov 12 08:17:41 +0100 2009:
Nicolas Pouillard wrote:
Excerpts from jean-christophe mincke's message of Tue Nov 10 21:18:34 +0100
2009:
do acc - get
put (acc+1)
...
Since this pattern occurs often 'modify' is a combination of
Excerpts from jean-christophe mincke's message of Tue Nov 10 21:18:34 +0100
2009:
Hello,
Hello,
I would like to get some advice about state monad (or any other monad I
guess) and CPS.
Here is to remarks somewhat off topic:
[...]
walk Empty acc k = k acc
walk (Leaf _) acc k = k (acc+1)
Nicolas Pouillard wrote:
Excerpts from jean-christophe mincke's message of Tue Nov 10 21:18:34 +0100
2009:
do acc - get
put (acc+1)
...
Since this pattern occurs often 'modify' is a combination of get and put:
do modify (+1)
...
Though the caveat about laziness applies here as
Hello,
I would like to get some advice about state monad (or any other monad I
guess) and CPS.
Let's take a simple exemple (see the code below)
'walk' is a function written in CPS that compute the number of nodes
leaves in a tree. It use a counter which is explicitly passed through calls.
Yes; check out the module Control.Monad.Cont, which has a monad for
continuation passing style.
In particular, note that most of the monads in Control.Monad.* are
stackable in that there is a version of the monad which you can
stack on top of an existing monad. So for example, you could
Something like this should work:
newtype ContState r s a = ContState { runCS :: s - (a - s - r) - r }
instance Monad (ContState r s) where
return a = ContState $ \s k - k a s
m = f = ContState $ \s0 k - runCS m s $ \a s1 - runCS (f a) s1 k
instance MonadState s (ContState r s) where
