{-# OPTIONS_HADDOCK show-extensions #-} -- | -- Module : Unbound.Generics.LocallyNameless.LFresh -- Copyright : (c) 2011, Stephanie Weirich -- License : BSD3 (See LFresh.hs) -- Maintainer : Aleksey Kliger -- Stability : experimental -- -- Local freshness monad. {- Copyright (c)2011, Stephanie Weirich All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of Stephanie Weirich nor the names of other contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. -} -- we expect deprecation warnings about Control.Monad.Trans.Error {-# OPTIONS_GHC -Wwarn #-} {-# LANGUAGE CPP , GeneralizedNewtypeDeriving , FlexibleInstances , MultiParamTypeClasses , UndecidableInstances #-} module Unbound.Generics.LocallyNameless.LFresh ( -- * The 'LFresh' class LFresh(..), LFreshM, runLFreshM, contLFreshM, LFreshMT(..), runLFreshMT, contLFreshMT ) where import Data.Set (Set) import qualified Data.Set as S import Data.Monoid import Data.Typeable (Typeable) import Control.Monad.Reader import Control.Monad.Identity import Control.Applicative (Applicative, Alternative) import Control.Monad.Trans.Cont import Control.Monad.Trans.Error import Control.Monad.Trans.Except import Control.Monad.Trans.Identity import Control.Monad.Trans.List import Control.Monad.Trans.Maybe import Control.Monad.Trans.State.Lazy as Lazy import Control.Monad.Trans.State.Strict as Strict import Control.Monad.Trans.Writer.Lazy as Lazy import Control.Monad.Trans.Writer.Strict as Strict import qualified Control.Monad.Cont.Class as CC import qualified Control.Monad.Error.Class as EC import qualified Control.Monad.State.Class as StC import qualified Control.Monad.Reader.Class as RC import qualified Control.Monad.Writer.Class as WC import Unbound.Generics.LocallyNameless.Name -- | This is the class of monads that support freshness in an -- (implicit) local scope. Generated names are fresh for the current -- local scope, not necessarily globally fresh. class Monad m => LFresh m where -- | Pick a new name that is fresh for the current (implicit) scope. lfresh :: Typeable a => Name a -> m (Name a) -- | Avoid the given names when freshening in the subcomputation, -- that is, add the given names to the in-scope set. avoid :: [AnyName] -> m a -> m a -- | Get the set of names currently being avoided. getAvoids :: m (Set AnyName) -- | The LFresh monad transformer. Keeps track of a set of names to -- avoid, and when asked for a fresh one will choose the first numeric -- prefix of the given name which is currently unused. newtype LFreshMT m a = LFreshMT { unLFreshMT :: ReaderT (Set AnyName) m a } deriving (Functor, Applicative, Alternative, Monad, MonadIO, MonadPlus, MonadFix) -- | Run an 'LFreshMT' computation in an empty context. runLFreshMT :: LFreshMT m a -> m a runLFreshMT m = contLFreshMT m S.empty -- | Run an 'LFreshMT' computation given a set of names to avoid. contLFreshMT :: LFreshMT m a -> Set AnyName -> m a contLFreshMT (LFreshMT m) = runReaderT m instance Monad m => LFresh (LFreshMT m) where lfresh nm = LFreshMT $ do let s = name2String nm used <- ask return $ head (filter (\x -> not (S.member (AnyName x) used)) (map (makeName s) [0..])) avoid names = LFreshMT . local (S.union (S.fromList names)) . unLFreshMT getAvoids = LFreshMT ask -- | A convenient monad which is an instance of 'LFresh'. It keeps -- track of a set of names to avoid, and when asked for a fresh one -- will choose the first unused numerical name. type LFreshM = LFreshMT Identity -- | Run a LFreshM computation in an empty context. runLFreshM :: LFreshM a -> a runLFreshM = runIdentity . runLFreshMT -- | Run a LFreshM computation given a set of names to avoid. contLFreshM :: LFreshM a -> Set AnyName -> a contLFreshM m = runIdentity . contLFreshMT m instance LFresh m => LFresh (ContT r m) where lfresh = lift . lfresh avoid = mapContT . avoid getAvoids = lift getAvoids instance (Error e, LFresh m) => LFresh (ErrorT e m) where lfresh = lift . lfresh avoid = mapErrorT . avoid getAvoids = lift getAvoids instance LFresh m => LFresh (ExceptT e m) where lfresh = lift . lfresh avoid = mapExceptT . avoid getAvoids = lift getAvoids instance LFresh m => LFresh (IdentityT m) where lfresh = lift . lfresh avoid = mapIdentityT . avoid getAvoids = lift getAvoids instance LFresh m => LFresh (ListT m) where lfresh = lift . lfresh avoid = mapListT . avoid getAvoids = lift getAvoids instance LFresh m => LFresh (MaybeT m) where lfresh = lift . lfresh avoid = mapMaybeT . avoid getAvoids = lift getAvoids instance LFresh m => LFresh (ReaderT r m) where lfresh = lift . lfresh avoid = mapReaderT . avoid getAvoids = lift getAvoids instance LFresh m => LFresh (Lazy.StateT s m) where lfresh = lift . lfresh avoid = Lazy.mapStateT . avoid getAvoids = lift getAvoids instance LFresh m => LFresh (Strict.StateT s m) where lfresh = lift . lfresh avoid = Strict.mapStateT . avoid getAvoids = lift getAvoids instance (Monoid w, LFresh m) => LFresh (Lazy.WriterT w m) where lfresh = lift . lfresh avoid = Lazy.mapWriterT . avoid getAvoids = lift getAvoids instance (Monoid w, LFresh m) => LFresh (Strict.WriterT w m) where lfresh = lift . lfresh avoid = Strict.mapWriterT . avoid getAvoids = lift getAvoids -- Instances for applying LFreshMT to other monads instance MonadTrans LFreshMT where lift = LFreshMT . lift instance CC.MonadCont m => CC.MonadCont (LFreshMT m) where callCC c = LFreshMT $ CC.callCC (unLFreshMT . (\k -> c (LFreshMT . k))) instance EC.MonadError e m => EC.MonadError e (LFreshMT m) where throwError = lift . EC.throwError catchError m h = LFreshMT $ EC.catchError (unLFreshMT m) (unLFreshMT . h) instance StC.MonadState s m => StC.MonadState s (LFreshMT m) where get = lift StC.get put = lift . StC.put instance RC.MonadReader r m => RC.MonadReader r (LFreshMT m) where ask = lift RC.ask local f = LFreshMT . mapReaderT (RC.local f) . unLFreshMT instance WC.MonadWriter w m => WC.MonadWriter w (LFreshMT m) where tell = lift . WC.tell listen = LFreshMT . WC.listen . unLFreshMT pass = LFreshMT . WC.pass . unLFreshMT