Thanks for the Cont example, David. But...
The MonadCont is clever and it works ... but then fails -- ghci does not garbage collect and it blows up.
With the MonadCont version I can count up to 10^7 zeros:
*Main> length $ take (10^7) zerosInf 10000000 (26.20 secs, 0 bytes)
But this increases RSIZE of ghc-6.4 to 165MB. The 10^8 version goes to swap space and I had to kill it. My original MonadWriter version does not increase RSIZE when run (constant space), so the garbage collection must be working, and it is O(N) in the # of zeros counted:
*Main> length $ take (10^7) zerosInf 10000000 (1.22 secs, 0 bytes) *Main> length $ take (10^8) zerosInf 100000000 (10.05 secs, 0 bytes) *Main> length $ take (10^9) zerosInf 1000000000 (109.83 secs, 6 bytes)
-- Chris
On Apr 14, 2005, at 1:05 AM, David Menendez wrote:
ChrisK writes:
I was thinking to myself: What in Haskell would give me a "yield" command like a Python generator?
And the answer was "tell" in Control.Monad.Writer -- and I wrote some simple examples (see below).
Another possibility would be a continuation monad.
import Control.Monad.Cont
yield :: a -> Cont [a] () yield x = Cont (\c -> x : c ())
asGenerator :: Cont [a] v -> [a]
asGenerator (Cont f) = f (const [])
--
David Menendez <[EMAIL PROTECTED]> | "In this house, we obey the laws
<http://www.eyrie.org/~zednenem> | of thermodynamics!"
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