Initial

1 files changed, 25 insertions, 0 deletions

diff --git a/SC/Monad.hs b/SC/Monad.hs
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index 0000000..c58755f
--- /dev/null
+++ b/SC/Monad.hs
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+{-# LANGUAGE DerivingVia #-}
+module SC.Monad where
+
+import Control.Monad.Trans.Class (lift)
+import Control.Monad.Trans.Except
+import Control.Monad.Trans.State.Strict
+
+
+newtype SC a = SC (ExceptT String (State Int) a)
+  deriving (Functor, Applicative, Monad) via (ExceptT String (State Int))
+
+instance MonadFail SC where
+    fail = throw
+
+evalSC :: SC a -> Either String a
+evalSC (SC m) = evalState (runExceptT m) 1
+
+genId :: SC Int
+genId = SC $ do
+    value <- lift get
+    lift (modify (+1))
+    return value
+
+throw :: String -> SC a
+throw = SC . throwE