hi kak On 30 May 2012, at 20:17, kak dod wrote:
. . . can you please remove the IO stuff from your first (non-state monadic) example and repost the same example again?
Sure. Here it is, with an essentially similar recursive design in the new non-IO, non-State-monad option. See if it makes any more sense.. br/ Henry -- -- Version 3 - containg two alternative "String -> String" solutions: -- 1) "ahaVanilla" does not use the State monad -- 2) "ahaStMonad" (was 'mystatemachine'in version 2) -- -- the substring "YYY*" followed by spaces (0+) will be found -- in the response string at the position corresponding to the first -- occurrence of substring "aha!" in the input string -- import Control.Monad.State type MyState = Char initstate, exitstate :: MyState initstate = 'a' exitstate = 'z' ahaVanilla :: String -> String ahaVanilla str = vanilla initstate str where vanilla _ [] = [] vanilla state (c:cs) = let (responsechar, nextstate) = stateMC c state in responsechar:( vanilla nextstate cs ) ahaStMonad :: String -> String ahaStMonad str = evalState ( mapM charfunc str ) initstate where charfunc :: Char -> State MyState Char charfunc c = state (stateMC c) stateMC :: Char -> MyState -> (Char, MyState) stateMC 'a' 'a' = ('Y', 'b') stateMC 'h' 'b' = ('Y', 'c') stateMC 'a' 'c' = ('Y', 'd') stateMC '!' 'd' = ('*', 'z') stateMC _ 'z' = (' ', 'z') stateMC _ _ = ('N', 'a')