add run1 run2 solution (#44)

Author: d1skort

MonadTransformers/4.5/stateList.hs

@@ -0,0 +1,31 @@
+{-# LANGUAGE FlexibleContexts #-}
+module StateList where
+
+import Control.Monad.Except
+import Control.Monad.State
+import Data.Foldable
+
+
+limited :: (MonadError Int m, MonadState s m) => (s -> Bool) -> [State s a] -> m [a]
+limited p fs = traverse limit1 (zip [0..] fs) where
+  limit1 (i, f) = do
+    a <- state (runState f)
+    stateIsBad <- gets (not . p)
+    when stateIsBad $ throwError i
+    return a
+
+
+runLimited1 :: (s -> Bool) -> [State s a] -> s -> (Either Int [a], s)
+runLimited1 p fs s = run1 (limited p fs) s
+
+
+runLimited2 :: (s -> Bool) -> [State s a] -> s -> Either Int ([a], s)
+runLimited2 p fs s = run2 (limited p fs) s
+
+
+run1 :: ExceptT Int (State s) [a] -> s -> (Either Int [a], s)
+run1 m s = runState (runExceptT m) s
+
+
+run2 :: StateT s (Except Int) [a] -> s -> Either Int ([a], s)
+run2 m s = runExcept $ runStateT m s