Modules and a main function

28 Aug 2011


      W/r/t the code below, would somebody please explain the sense of having a main function in a module that is not named Main.hs?

Michael

From: http://www.haskell.org/haskellwiki/State_Monad

============
module StateGame where

 
import Control.Monad.State
 
-- Example use of State monad
-- Passes a string of dictionary {a,b,c}
-- Game is to produce a number from the string.
-- By default the game is off, a C toggles the
-- game on and off. A 'a' gives +1 and a b gives -1.
-- E.g 
-- 'ab'    = 0
-- 'ca'    = 1
-- 'cabca' = 0
-- State = game is on or off & current score
--       = (Bool, Int)
 
type GameValue = Int
type GameState = (Bool, Int)
 
playGame :: String -> State GameState GameValue
playGame []     = do
    (_, score) <- get
    return score
 
playGame (x:xs) = do
    (on, score) <- get
    case x of
         'a' | on -> put (on, score + 1)
         'b' | on -> put (on, score - 1)
         'c'      -> put (not on, score)
         _        -> put (on, score)
    playGame xs
 
startState = (False, 0)
 
main = print $ evalState (playGame "abcaaacbbcabbab") startState

michael rice

Brandon Allbery

michael rice

Daniel Fischer

michael rice

Brandon Allbery

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