GotoT-transformers (empty) → 1.0

raw patch · 4 files changed

+144/−0 lines, 4 filesdep +basedep +transformerssetup-changed

Dependencies added: base, transformers

Files

Control/Monad/Trans/Goto.hs +102/−0
GotoT-transformers.cabal +18/−0
LICENSE +22/−0
Setup.hs +2/−0

+ Control/Monad/Trans/Goto.hs view

@@ -0,0 +1,102 @@+-----------------------------------------------------------------------------+-- |+-- Module      :  Control.Monad.Trans.Goto+-- Copyright   :  (c) Gregory Crosswhite 2001+-- License     :  BSD3+-- Maintainer  :  gcross@phys.washington.edu+-- Stability   :  provisional+-- Portability :  portable+--+-- This module provides a monad and a monad transformer that allow the+-- user to transfer the flow of execution from an arbitrary point of a+-- monadic computation to another monadic computation.+-----------------------------------------------------------------------------+++module Control.Monad.Trans.Goto (+    -- * The Goto monad+    Goto,+    runGoto,+    -- * The GotoT monad transformer+    GotoT(..),+    runGotoT,+    -- * Goto operations+    goto+    ) where++import Control.Applicative (Applicative(..),(<*>))+import Control.Monad.IO.Class (MonadIO(..))+import Control.Monad.Trans.Class (MonadTrans(..))++import Data.Functor+import Data.Functor.Identity++-- ---------------------------------------------------------------------------+-- | A goto monad, parameterized by the type @r@ of the value to return.+type Goto r = GotoT r Identity++-- | Execute the goto monad computation and return the resulting value.+runGoto :: Goto r r -- ^ the monadic computation to run+        -> r        -- ^ the result of the computation+runGoto = runIdentity . runGotoT++-- ---------------------------------------------------------------------------+-- | A goto monad transformer parameterized by+--+--   * @r@ - the value that will ultimately be returned; and+--+--   * @m@ - the inner monad.+--+-- The 'GotoT' type wraps a monadic value that contains either a pure value or+-- the next place at which the flow of execution should be continued.+newtype GotoT r m a = GotoT { unwrapGotoT :: m (Either (GotoT r m r) a) }++instance Applicative m => Applicative (GotoT r m) where+    pure = GotoT . fmap Right . pure+    (GotoT m) <*> (GotoT x) = GotoT ((fmap h m) <*> x)+      where+        h (Left g) = const (Left g)+        h (Right f) = either Left (Right . f)+instance Functor m => Functor (GotoT r m) where+    fmap f = GotoT . fmap (either Left (Right . f)) . unwrapGotoT+instance Monad m => Monad (GotoT r m) where+    return = GotoT . return . Right+    (GotoT m) >>= f = GotoT $ m >>= either (return . Left) (unwrapGotoT . f)+instance MonadIO m => MonadIO (GotoT r m) where+    liftIO = lift . liftIO+instance MonadTrans (GotoT r) where+    lift = GotoT . (>>= return . Right)++-- | Execute the goto monad computation and return the resulting value.+--+-- 'runGotoT' is implemented by using a ''trampoline'' approach.  It+-- looks at the monadic value and checks whether it is either a 'Left'+-- containing a continuation or a 'Right' containing the result.  As+-- long as it sees a 'Left' it executes the continuation and then+-- feeds the result back into itself.  Thus the computation bounces+-- back to this function (hence the ''trampoline'') as long as the+-- user keeps calling 'goto' until the final result has been obtained.+runGotoT :: Monad m+         => GotoT r m r -- ^ the monadic computation to run+         -> m r         -- ^ the result of the computation+runGotoT (GotoT m) = m >>= either runGotoT return++-- ---------------------------------------------------------------------------+-- | Transfer the flow of executation from an arbitrary point in the current+--   monadic computation to another monadic computation.+--+-- Note that the destination computation must promise to produce the+-- same value that was promised to be returned by the origin+-- computation.  Also, since control is being transferred away from+-- the origin computation, the goto function returns a monadic value that+-- can have an arbitrary type, since the monadic value will never+-- be used by the originating computation.+goto :: Monad m+     => GotoT r m r -- ^ the destination to which to transfer the flow+                    --   of execution+     -> GotoT r m a -- ^ a monadic value that has the effect of+                    --   transferring the flow of execution to the+                    --   specified destination; note that value can+                    --   have an arbitrary type since it will never+                    --   actually be accessed+goto = GotoT . return . Left

+ GotoT-transformers.cabal view

@@ -0,0 +1,18 @@+Name:                GotoT-transformers+Version:             1.0+License:             BSD3+License-file:        LICENSE+Author:              Gregory Crosswhite+Maintainer:          Gregory Crosswhite <gcross@phys.washington.edu>+Stability:           Provisional+Homepage:            http://github.com/gcross/GotoT-transformers+Synopsis:            A monad and monadic transformer providing "goto" functionality+Description:         This module provides a monad and a monad transformer that allow the user to transfer the flow of execution from an arbitrary point of a monadic computation to another monadic computation.+Cabal-version:       >=1.2.3+Build-type:          Simple+Category:	     Control++Library+    Build-depends:   base >= 3 && < 5,+                     transformers >= 0.2 && <0.3+    Exposed-modules: Control.Monad.Trans.Goto

+ LICENSE view

@@ -0,0 +1,22 @@+Copyright (c) 2010, Gregory Crosswhite+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.++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.

+ Setup.hs view

@@ -0,0 +1,2 @@+import Distribution.Simple+main = defaultMain