git.iko.soy/rowtype-yoga/purescript-native
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rowtype-yoga/purescript-native/src/PureScript/TypeChecker/Monad.hs
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1-----------------------------------------------------------------------------
2--
3-- Module : PureScript.TypeChecker.Monad
4-- Copyright : (c) Phil Freeman 2013
5-- License : MIT
6--
7-- Maintainer : Phil Freeman <paf31@cantab.net>
8-- Stability : experimental
9-- Portability :
10--
11-- |
12--
13-----------------------------------------------------------------------------
15{-# LANGUAGE GeneralizedNewtypeDeriving, FlexibleInstances #-}
17module PureScript.TypeChecker.Monad where
19import PureScript.Types
20import PureScript.Kinds
22import Control.Applicative
23import Control.Monad.State
24import Control.Monad.Error
26import Control.Arrow ((***))
28import qualified Data.Map as M
30data Environment = Environment
31 { names :: M.Map String Type
32 , types :: M.Map String Kind
33 } deriving (Show)
35emptyEnvironment :: Environment
36emptyEnvironment = Environment M.empty M.empty
38newtype Check a = Check { unCheck :: StateT (Environment, Int) (Either String) a } deriving (Functor, Monad, Applicative, MonadPlus, MonadState (Environment, Int), MonadError String)
40getEnv :: Check Environment
41getEnv = fmap fst get
43putEnv :: Environment -> Check ()
44putEnv env = fmap (const env *** id) get >>= put
46fresh :: Check Int
47fresh = do
48 (env, n) <- get
49 put (env, n + 1)
50 return n
52check :: Check a -> Either String (a, Environment)
53check = fmap (id *** fst) . flip runStateT (emptyEnvironment, 0) . unCheck
55guardWith :: (MonadError e m) => e -> Bool -> m ()
56guardWith _ True = return ()
57guardWith e False = throwError e
59rethrow :: (MonadError e m) => (e -> e) -> m a -> m a
60rethrow f = flip catchError $ \e -> throwError (f e)