46 lines
1.1 KiB
Haskell
46 lines
1.1 KiB
Haskell
{-# LANGUAGE AllowAmbiguousTypes #-}
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{-# LANGUAGE ConstraintKinds #-}
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{-# LANGUAGE DeriveFoldable #-}
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{-# LANGUAGE DeriveFunctor #-}
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{-# LANGUAGE DeriveTraversable #-}
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{-# LANGUAGE FlexibleContexts #-}
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{-# LANGUAGE ScopedTypeVariables #-}
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{-# OPTIONS_GHC -Wno-orphans #-}
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module Nix.Var where
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import Control.Monad.Ref
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import Data.GADT.Compare
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import Data.IORef
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import Data.Maybe
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import Data.STRef
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import Unsafe.Coerce
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type Var m = Ref m
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type MonadVar m = MonadAtomicRef m
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eqVar :: forall m a . GEq (Ref m) => Ref m a -> Ref m a -> Bool
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eqVar a b = isJust $ geq a b
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newVar :: MonadRef m => a -> m (Ref m a)
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newVar = newRef
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readVar :: MonadRef m => Ref m a -> m a
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readVar = readRef
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writeVar :: MonadRef m => Ref m a -> a -> m ()
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writeVar = writeRef
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atomicModifyVar :: MonadAtomicRef m => Ref m a -> (a -> (a, b)) -> m b
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atomicModifyVar = atomicModifyRef
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--TODO: Upstream GEq instances
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instance GEq IORef where
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a `geq` b = if a == unsafeCoerce b then Just $ unsafeCoerce Refl else Nothing
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instance GEq (STRef s) where
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a `geq` b = if a == unsafeCoerce b then Just $ unsafeCoerce Refl else Nothing
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