On Thursday 13 January 2011 21:17:41, michael rice wrote:
{- From: http://en.wikibooks.org/wiki/Haskell/Monad_transformers if for instance we apply StateT to the List monad, a function that returns a list (i.e., a computation in the List monad) can be lifted into StateT s [], where it becomes a function that returns a StateT (s -> [(a,s)]). That is, the lifted computation produces multiple (value,state) pairs from its input state. -}
import Control.Monad.Trans.State.Lazy
type GeneratorState = StateT Int
-- a function in the list monad f :: Int -> [Int] f n = [0..n]
Will someone please demonstrate the above comment from the wiki page.
lift (f n) = StateT (\s -> [(k,s) | k <- [0 .. n]]) Generally, lift list = StateT (\s -> zip list (repeat s))
Michael