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<pre><a name="line-1"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-2"></a><span class='hs-comment'>-- |</span>
<a name="line-3"></a><span class='hs-comment'>-- Module : Control.Monad.Trans.Cont</span>
<a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) The University of Glasgow 2001</span>
<a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the file LICENSE)</span>
<a name="line-6"></a><span class='hs-comment'>--</span>
<a name="line-7"></a><span class='hs-comment'>-- Maintainer : ross@soi.city.ac.uk</span>
<a name="line-8"></a><span class='hs-comment'>-- Stability : experimental</span>
<a name="line-9"></a><span class='hs-comment'>-- Portability : portable</span>
<a name="line-10"></a><span class='hs-comment'>--</span>
<a name="line-11"></a><span class='hs-comment'>-- Continuation monads.</span>
<a name="line-12"></a><span class='hs-comment'>--</span>
<a name="line-13"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-14"></a>
<a name="line-15"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Cont</span> <span class='hs-layout'>(</span>
<a name="line-16"></a> <span class='hs-comment'>-- * The Cont monad</span>
<a name="line-17"></a> <span class='hs-conid'>Cont</span><span class='hs-layout'>,</span>
<a name="line-18"></a> <span class='hs-varid'>cont</span><span class='hs-layout'>,</span>
<a name="line-19"></a> <span class='hs-varid'>runCont</span><span class='hs-layout'>,</span>
<a name="line-20"></a> <span class='hs-varid'>mapCont</span><span class='hs-layout'>,</span>
<a name="line-21"></a> <span class='hs-varid'>withCont</span><span class='hs-layout'>,</span>
<a name="line-22"></a> <span class='hs-comment'>-- * The ContT monad transformer</span>
<a name="line-23"></a> <span class='hs-conid'>ContT</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-24"></a> <span class='hs-varid'>mapContT</span><span class='hs-layout'>,</span>
<a name="line-25"></a> <span class='hs-varid'>withContT</span><span class='hs-layout'>,</span>
<a name="line-26"></a> <span class='hs-varid'>callCC</span><span class='hs-layout'>,</span>
<a name="line-27"></a> <span class='hs-comment'>-- * Lifting other operations</span>
<a name="line-28"></a> <span class='hs-varid'>liftLocal</span><span class='hs-layout'>,</span>
<a name="line-29"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-30"></a>
<a name="line-31"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span>
<a name="line-32"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span>
<a name="line-33"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Functor</span><span class='hs-varop'>.</span><span class='hs-conid'>Identity</span>
<a name="line-34"></a>
<a name="line-35"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Applicative</span>
<a name="line-36"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span>
<a name="line-37"></a>
<a name="line-38"></a><a name="Cont"></a><span class='hs-comment'>{- |
<a name="line-39"></a>Continuation monad.
<a name="line-40"></a>@Cont r a@ is a CPS computation that produces an intermediate result
<a name="line-41"></a>of type @a@ within a CPS computation whose final result type is @r@.
<a name="line-42"></a>
<a name="line-43"></a>The @return@ function simply creates a continuation which passes the value on.
<a name="line-44"></a>
<a name="line-45"></a>The @>>=@ operator adds the bound function into the continuation chain.
<a name="line-46"></a>-}</span>
<a name="line-47"></a><a name="Cont"></a><span class='hs-keyword'>type</span> <span class='hs-conid'>Cont</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-conid'>Identity</span>
<a name="line-48"></a>
<a name="line-49"></a><a name="cont"></a><span class='hs-comment'>-- | Construct a continuation-passing computation from a function.</span>
<a name="line-50"></a><span class='hs-comment'>-- (The inverse of 'runCont'.)</span>
<a name="line-51"></a><span class='hs-definition'>cont</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Cont</span> <span class='hs-varid'>r</span> <span class='hs-varid'>a</span>
<a name="line-52"></a><span class='hs-definition'>cont</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Identity</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-varid'>runIdentity</span> <span class='hs-varop'>.</span> <span class='hs-varid'>k</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-53"></a>
<a name="line-54"></a><a name="runCont"></a><span class='hs-comment'>-- | Runs a CPS computation, returns its result after applying the final</span>
<a name="line-55"></a><span class='hs-comment'>-- continuation to it.</span>
<a name="line-56"></a><span class='hs-comment'>-- (The inverse of 'cont'.)</span>
<a name="line-57"></a><span class='hs-definition'>runCont</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Cont</span> <span class='hs-varid'>r</span> <span class='hs-varid'>a</span> <span class='hs-comment'>-- ^ continuation computation (@Cont@).</span>
<a name="line-58"></a> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ the final continuation, which produces</span>
<a name="line-59"></a> <span class='hs-comment'>-- the final result (often 'id').</span>
<a name="line-60"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span>
<a name="line-61"></a><span class='hs-definition'>runCont</span> <span class='hs-varid'>m</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>runIdentity</span> <span class='hs-layout'>(</span><span class='hs-varid'>runContT</span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-conid'>Identity</span> <span class='hs-varop'>.</span> <span class='hs-varid'>k</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-62"></a>
<a name="line-63"></a><a name="mapCont"></a><span class='hs-definition'>mapCont</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Cont</span> <span class='hs-varid'>r</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Cont</span> <span class='hs-varid'>r</span> <span class='hs-varid'>a</span>
<a name="line-64"></a><span class='hs-definition'>mapCont</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mapContT</span> <span class='hs-layout'>(</span><span class='hs-conid'>Identity</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span> <span class='hs-varop'>.</span> <span class='hs-varid'>runIdentity</span><span class='hs-layout'>)</span>
<a name="line-65"></a>
<a name="line-66"></a><a name="withCont"></a><span class='hs-definition'>withCont</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Cont</span> <span class='hs-varid'>r</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Cont</span> <span class='hs-varid'>r</span> <span class='hs-varid'>b</span>
<a name="line-67"></a><span class='hs-definition'>withCont</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>withContT</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-conid'>Identity</span> <span class='hs-varop'>.</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span> <span class='hs-varop'>.</span> <span class='hs-layout'>(</span><span class='hs-varid'>runIdentity</span> <span class='hs-varop'>.</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-68"></a>
<a name="line-69"></a><a name="ContT"></a><span class='hs-comment'>{- |
<a name="line-70"></a>The continuation monad transformer.
<a name="line-71"></a>Can be used to add continuation handling to other monads.
<a name="line-72"></a>-}</span>
<a name="line-73"></a><a name="ContT"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-layout'>{</span> <span class='hs-varid'>runContT</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span> <span class='hs-layout'>}</span>
<a name="line-74"></a>
<a name="line-75"></a><a name="mapContT"></a><span class='hs-definition'>mapContT</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-varid'>m</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-76"></a><span class='hs-definition'>mapContT</span> <span class='hs-varid'>f</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-varid'>f</span> <span class='hs-varop'>.</span> <span class='hs-varid'>runContT</span> <span class='hs-varid'>m</span>
<a name="line-77"></a>
<a name="line-78"></a><a name="withContT"></a><span class='hs-definition'>withContT</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span>
<a name="line-79"></a><span class='hs-definition'>withContT</span> <span class='hs-varid'>f</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-varid'>runContT</span> <span class='hs-varid'>m</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span>
<a name="line-80"></a>
<a name="line-81"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Functor</span> <span class='hs-layout'>(</span><span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-82"></a> <span class='hs-varid'>fmap</span> <span class='hs-varid'>f</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>c</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runContT</span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-varid'>c</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span>
<a name="line-83"></a>
<a name="line-84"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Applicative</span> <span class='hs-layout'>(</span><span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-85"></a> <span class='hs-varid'>pure</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-layout'>(</span><span class='hs-varop'>$</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-86"></a> <span class='hs-varid'>f</span> <span class='hs-varop'><*></span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runContT</span> <span class='hs-varid'>f</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runContT</span> <span class='hs-varid'>v</span> <span class='hs-layout'>(</span><span class='hs-varid'>k</span> <span class='hs-varop'>.</span> <span class='hs-varid'>g</span><span class='hs-layout'>)</span>
<a name="line-87"></a>
<a name="line-88"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-89"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-layout'>(</span><span class='hs-varop'>$</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span>
<a name="line-90"></a> <span class='hs-varid'>m</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>c</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runContT</span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runContT</span> <span class='hs-layout'>(</span><span class='hs-varid'>k</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span>
<a name="line-91"></a>
<a name="line-92"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadTrans</span> <span class='hs-layout'>(</span><span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-93"></a> <span class='hs-varid'>lift</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-layout'>(</span><span class='hs-varid'>m</span> <span class='hs-varop'>>>=</span><span class='hs-layout'>)</span>
<a name="line-94"></a>
<a name="line-95"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadIO</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadIO</span> <span class='hs-layout'>(</span><span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-96"></a> <span class='hs-varid'>liftIO</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varop'>.</span> <span class='hs-varid'>liftIO</span>
<a name="line-97"></a>
<a name="line-98"></a><a name="callCC"></a><span class='hs-comment'>-- | @callCC@ (call-with-current-continuation) calls its argument</span>
<a name="line-99"></a><span class='hs-comment'>-- function, passing it the current continuation. It provides</span>
<a name="line-100"></a><span class='hs-comment'>-- an escape continuation mechanism for use with continuation</span>
<a name="line-101"></a><span class='hs-comment'>-- monads. Escape continuations one allow to abort the current</span>
<a name="line-102"></a><span class='hs-comment'>-- computation and return a value immediately. They achieve a</span>
<a name="line-103"></a><span class='hs-comment'>-- similar effect to 'Control.Monad.Trans.Error.throwError'</span>
<a name="line-104"></a><span class='hs-comment'>-- and 'Control.Monad.Trans.Error.catchError' within an</span>
<a name="line-105"></a><span class='hs-comment'>-- 'Control.Monad.Trans.Error.ErrorT' monad. The advantage of this</span>
<a name="line-106"></a><span class='hs-comment'>-- function over calling 'return' is that it makes the continuation</span>
<a name="line-107"></a><span class='hs-comment'>-- explicit, allowing more flexibility and better control.</span>
<a name="line-108"></a><span class='hs-comment'>--</span>
<a name="line-109"></a><span class='hs-comment'>-- The standard idiom used with @callCC@ is to provide a lambda-expression</span>
<a name="line-110"></a><span class='hs-comment'>-- to name the continuation. Then calling the named continuation anywhere</span>
<a name="line-111"></a><span class='hs-comment'>-- within its scope will escape from the computation, even if it is many</span>
<a name="line-112"></a><span class='hs-comment'>-- layers deep within nested computations.</span>
<a name="line-113"></a><span class='hs-definition'>callCC</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-114"></a><span class='hs-definition'>callCC</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>c</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>runContT</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>c</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-varid'>c</span>
<a name="line-115"></a>
<a name="line-116"></a><a name="liftLocal"></a><span class='hs-comment'>-- | @'liftLocal' ask local@ yields a @local@ function for @'ContT' r m@.</span>
<a name="line-117"></a><span class='hs-definition'>liftLocal</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r'</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>r'</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span>
<a name="line-118"></a> <span class='hs-layout'>(</span><span class='hs-varid'>r'</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ContT</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-119"></a><span class='hs-definition'>liftLocal</span> <span class='hs-varid'>ask</span> <span class='hs-varid'>local</span> <span class='hs-varid'>f</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ContT</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>c</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-120"></a> <span class='hs-varid'>r</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>ask</span>
<a name="line-121"></a> <span class='hs-varid'>local</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-varid'>runContT</span> <span class='hs-varid'>m</span> <span class='hs-layout'>(</span><span class='hs-varid'>local</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
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