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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE UndecidableInstances #-}</span>
<a name="line-2"></a><span class='hs-comment'>-- Search for UndecidableInstances to see why this is needed</span>
<a name="line-3"></a><span class='hs-comment'>{- |
<a name="line-4"></a>Module : Control.Monad.Reader.Class
<a name="line-5"></a>Copyright : (c) Andy Gill 2001,
<a name="line-6"></a> (c) Oregon Graduate Institute of Science and Technology 2001,
<a name="line-7"></a> (c) Jeff Newbern 2003-2007,
<a name="line-8"></a> (c) Andriy Palamarchuk 2007
<a name="line-9"></a>License : BSD-style (see the file LICENSE)
<a name="line-10"></a>
<a name="line-11"></a>Maintainer : libraries@haskell.org
<a name="line-12"></a>Stability : experimental
<a name="line-13"></a>Portability : non-portable (multi-param classes, functional dependencies)
<a name="line-14"></a>
<a name="line-15"></a>[Computation type:] Computations which read values from a shared environment.
<a name="line-16"></a>
<a name="line-17"></a>[Binding strategy:] Monad values are functions from the environment to a value.
<a name="line-18"></a>The bound function is applied to the bound value, and both have access
<a name="line-19"></a>to the shared environment.
<a name="line-20"></a>
<a name="line-21"></a>[Useful for:] Maintaining variable bindings, or other shared environment.
<a name="line-22"></a>
<a name="line-23"></a>[Zero and plus:] None.
<a name="line-24"></a>
<a name="line-25"></a>[Example type:] @'Reader' [(String,Value)] a@
<a name="line-26"></a>
<a name="line-27"></a>The 'Reader' monad (also called the Environment monad).
<a name="line-28"></a>Represents a computation, which can read values from
<a name="line-29"></a>a shared environment, pass values from function to function,
<a name="line-30"></a>and execute sub-computations in a modified environment.
<a name="line-31"></a>Using 'Reader' monad for such computations is often clearer and easier
<a name="line-32"></a>than using the 'Control.Monad.State.State' monad.
<a name="line-33"></a>
<a name="line-34"></a> Inspired by the paper
<a name="line-35"></a> /Functional Programming with Overloading and Higher-Order Polymorphism/,
<a name="line-36"></a> Mark P Jones (<<a href="http://web.cecs.pdx.edu/~mpj/">http://web.cecs.pdx.edu/~mpj/</a>>)
<a name="line-37"></a> Advanced School of Functional Programming, 1995.
<a name="line-38"></a>-}</span>
<a name="line-39"></a>
<a name="line-40"></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'>Reader</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span> <span class='hs-layout'>(</span>
<a name="line-41"></a> <span class='hs-conid'>MonadReader</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span>
<a name="line-42"></a> <span class='hs-varid'>asks</span><span class='hs-layout'>,</span>
<a name="line-43"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-44"></a>
<a name="line-45"></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'>Cont</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Cont</span>
<a name="line-46"></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'>Error</span>
<a name="line-47"></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'>Identity</span>
<a name="line-48"></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'>List</span>
<a name="line-49"></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'>Maybe</span>
<a name="line-50"></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'>Reader</span> <span class='hs-layout'>(</span><span class='hs-conid'>ReaderT</span><span class='hs-layout'>)</span>
<a name="line-51"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</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'>Reader</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>ReaderT</span> <span class='hs-layout'>(</span><span class='hs-varid'>ask</span><span class='hs-layout'>,</span> <span class='hs-varid'>local</span><span class='hs-layout'>)</span>
<a name="line-52"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</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'>RWS</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>LazyRWS</span> <span class='hs-layout'>(</span><span class='hs-conid'>RWST</span><span class='hs-layout'>,</span> <span class='hs-varid'>ask</span><span class='hs-layout'>,</span> <span class='hs-varid'>local</span><span class='hs-layout'>)</span>
<a name="line-53"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</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'>RWS</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>StrictRWS</span> <span class='hs-layout'>(</span><span class='hs-conid'>RWST</span><span class='hs-layout'>,</span> <span class='hs-varid'>ask</span><span class='hs-layout'>,</span> <span class='hs-varid'>local</span><span class='hs-layout'>)</span>
<a name="line-54"></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'>State</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Lazy</span>
<a name="line-55"></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'>State</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Strict</span>
<a name="line-56"></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'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Lazy</span>
<a name="line-57"></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'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Strict</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Strict</span>
<a name="line-58"></a>
<a name="line-59"></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> <span class='hs-layout'>(</span><span class='hs-varid'>lift</span><span class='hs-layout'>)</span>
<a name="line-60"></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-61"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Monoid</span>
<a name="line-62"></a>
<a name="line-63"></a><span class='hs-comment'>-- ----------------------------------------------------------------------------</span>
<a name="line-64"></a><span class='hs-comment'>-- class MonadReader</span>
<a name="line-65"></a><span class='hs-comment'>-- asks for the internal (non-mutable) state.</span>
<a name="line-66"></a>
<a name="line-67"></a><a name="MonadReader"></a><span class='hs-comment'>-- | See examples in "Control.Monad.Reader".</span>
<a name="line-68"></a><a name="MonadReader"></a><span class='hs-comment'>-- Note, the partially applied function type @(->) r@ is a simple reader monad.</span>
<a name="line-69"></a><a name="MonadReader"></a><span class='hs-comment'>-- See the @instance@ declaration below.</span>
<a name="line-70"></a><a name="MonadReader"></a><span class='hs-keyword'>class</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span> <span class='hs-keyword'>where</span>
<a name="line-71"></a> <span class='hs-comment'>-- | Retrieves the monad environment.</span>
<a name="line-72"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>m</span> <span class='hs-varid'>r</span>
<a name="line-73"></a>
<a name="line-74"></a> <span class='hs-comment'>-- | Executes a computation in a modified environment.</span>
<a name="line-75"></a> <span class='hs-varid'>local</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-comment'>-- ^ The function to modify the environment.</span>
<a name="line-76"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span> <span class='hs-comment'>-- ^ @Reader@ to run in the modified environment.</span>
<a name="line-77"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-78"></a>
<a name="line-79"></a><a name="asks"></a><span class='hs-comment'>-- | Retrieves a function of the current environment.</span>
<a name="line-80"></a><span class='hs-definition'>asks</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span>
<a name="line-81"></a> <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'>a</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- ^ The selector function to apply to the environment.</span>
<a name="line-82"></a> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-83"></a><span class='hs-definition'>asks</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-84"></a> <span class='hs-varid'>r</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>ask</span>
<a name="line-85"></a> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span>
<a name="line-86"></a>
<a name="line-87"></a><span class='hs-comment'>-- ----------------------------------------------------------------------------</span>
<a name="line-88"></a><span class='hs-comment'>-- The partially applied function type is a simple reader monad</span>
<a name="line-89"></a>
<a name="line-90"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadReader</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-layout'>)</span> <span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-91"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>id</span>
<a name="line-92"></a> <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-varid'>m</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span>
<a name="line-93"></a>
<a name="line-94"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>ReaderT</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-95"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ReaderT</span><span class='hs-varop'>.</span><span class='hs-varid'>ask</span>
<a name="line-96"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ReaderT</span><span class='hs-varop'>.</span><span class='hs-varid'>local</span>
<a name="line-97"></a>
<a name="line-98"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>LazyRWS</span><span class='hs-varop'>.</span><span class='hs-conid'>RWST</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-99"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyRWS</span><span class='hs-varop'>.</span><span class='hs-varid'>ask</span>
<a name="line-100"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>LazyRWS</span><span class='hs-varop'>.</span><span class='hs-varid'>local</span>
<a name="line-101"></a>
<a name="line-102"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>StrictRWS</span><span class='hs-varop'>.</span><span class='hs-conid'>RWST</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-103"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictRWS</span><span class='hs-varop'>.</span><span class='hs-varid'>ask</span>
<a name="line-104"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>StrictRWS</span><span class='hs-varop'>.</span><span class='hs-varid'>local</span>
<a name="line-105"></a>
<a name="line-106"></a><span class='hs-comment'>-- ---------------------------------------------------------------------------</span>
<a name="line-107"></a><span class='hs-comment'>-- Instances for other mtl transformers</span>
<a name="line-108"></a><span class='hs-comment'>--</span>
<a name="line-109"></a><span class='hs-comment'>-- All of these instances need UndecidableInstances,</span>
<a name="line-110"></a><span class='hs-comment'>-- because they do not satisfy the coverage condition.</span>
<a name="line-111"></a>
<a name="line-112"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r'</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r'</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-113"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-114"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Cont</span><span class='hs-varop'>.</span><span class='hs-varid'>liftLocal</span> <span class='hs-varid'>ask</span> <span class='hs-varid'>local</span>
<a name="line-115"></a>
<a name="line-116"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Error</span> <span class='hs-varid'>e</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorT</span> <span class='hs-varid'>e</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-117"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-118"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mapErrorT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
<a name="line-119"></a>
<a name="line-120"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>IdentityT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-121"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-122"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mapIdentityT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
<a name="line-123"></a>
<a name="line-124"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>ListT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-125"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-126"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mapListT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
<a name="line-127"></a>
<a name="line-128"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>MaybeT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-129"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-130"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>mapMaybeT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
<a name="line-131"></a>
<a name="line-132"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>Lazy</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-133"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-134"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Lazy</span><span class='hs-varop'>.</span><span class='hs-varid'>mapStateT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
<a name="line-135"></a>
<a name="line-136"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>Strict</span><span class='hs-varop'>.</span><span class='hs-conid'>StateT</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-137"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-138"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Strict</span><span class='hs-varop'>.</span><span class='hs-varid'>mapStateT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
<a name="line-139"></a>
<a name="line-140"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>Lazy</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>w</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-141"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-142"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Lazy</span><span class='hs-varop'>.</span><span class='hs-varid'>mapWriterT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
<a name="line-143"></a>
<a name="line-144"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>w</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>Strict</span><span class='hs-varop'>.</span><span class='hs-conid'>WriterT</span> <span class='hs-varid'>w</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-145"></a> <span class='hs-varid'>ask</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>ask</span>
<a name="line-146"></a> <span class='hs-varid'>local</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Strict</span><span class='hs-varop'>.</span><span class='hs-varid'>mapWriterT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>local</span>
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