83 lines
1.9 KiB
Haskell
83 lines
1.9 KiB
Haskell
{-# LANGUAGE CPP #-}
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{-# LANGUAGE DeriveFunctor #-}
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{-# LANGUAGE FlexibleContexts #-}
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{-# LANGUAGE FlexibleInstances #-}
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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
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{-# LANGUAGE MultiParamTypeClasses #-}
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{-# LANGUAGE RankNTypes #-}
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{-# LANGUAGE TypeFamilies #-}
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{-# LANGUAGE UndecidableInstances #-}
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{-# OPTIONS_GHC -Wno-orphans #-}
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module Nix.Fresh where
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import Control.Applicative
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import Control.Monad.Base
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import Control.Monad.Catch
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import Control.Monad.Except
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#if !MIN_VERSION_base(4,13,0)
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import Control.Monad.Fail
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#endif
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import Control.Monad.Reader
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import Control.Monad.Ref
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import Control.Monad.ST
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import Data.Typeable
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import Nix.Var
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import Nix.Thunk
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newtype FreshIdT i m a = FreshIdT { unFreshIdT :: ReaderT (Var m i) m a }
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deriving
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( Functor
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, Applicative
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, Alternative
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, Monad
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, MonadFail
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, MonadPlus
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, MonadFix
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, MonadRef
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, MonadAtomicRef
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, MonadIO
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, MonadCatch
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, MonadThrow
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, MonadMask
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)
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instance MonadTrans (FreshIdT i) where
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lift = FreshIdT . lift
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instance MonadBase b m => MonadBase b (FreshIdT i m) where
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liftBase = FreshIdT . liftBase
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instance ( MonadVar m
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, Eq i
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, Ord i
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, Show i
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, Enum i
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, Typeable i
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)
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=> MonadThunkId (FreshIdT i m) where
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type ThunkId (FreshIdT i m) = i
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freshId = FreshIdT $ do
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v <- ask
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atomicModifyVar v (\i -> (succ i, i))
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runFreshIdT :: Functor m => Var m i -> FreshIdT i m a -> m a
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runFreshIdT i m = runReaderT (unFreshIdT m) i
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-- Orphan instance needed by Infer.hs and Lint.hs
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-- Since there's no forking, it's automatically atomic.
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instance MonadAtomicRef (ST s) where
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atomicModifyRef r f = do
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v <- readRef r
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let (a, b) = f v
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writeRef r a
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return b
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atomicModifyRef' r f = do
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v <- readRef r
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let (a, b) = f v
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writeRef r $! a
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return b
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