Simple StateT use
Revision as of 01:51, 13 November 2006 by DonStewart (document StateT example)
A small example showing how to combine a State monad (in this case a unique supply), with the IO monad, via a monad transformer.
No need to resort to nasty mutable variables or globals!
import Control.Monad.State main = runStateT code [1..] >> return () -- -- layer a infinite list of uniques over the IO monad -- code = do x <- pop io $ print x y <- pop io $ print y return () -- -- pop the next unique off the stack -- pop = do (x:xs) <- get put xs return x io = liftIO