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<title>Control/Monad/RWS/Class.hs</title>
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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>
<a name="line-4"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-5"></a><span class='hs-comment'>-- |</span>
<a name="line-6"></a><span class='hs-comment'>-- Module : Control.Monad.RWS.Class</span>
<a name="line-7"></a><span class='hs-comment'>-- Copyright : (c) Andy Gill 2001,</span>
<a name="line-8"></a><span class='hs-comment'>-- (c) Oregon Graduate Institute of Science and Technology, 2001</span>
<a name="line-9"></a><span class='hs-comment'>-- License : BSD-style (see the file LICENSE)</span>
<a name="line-10"></a><span class='hs-comment'>--</span>
<a name="line-11"></a><span class='hs-comment'>-- Maintainer : libraries@haskell.org</span>
<a name="line-12"></a><span class='hs-comment'>-- Stability : experimental</span>
<a name="line-13"></a><span class='hs-comment'>-- Portability : non-portable (multi-param classes, functional dependencies)</span>
<a name="line-14"></a><span class='hs-comment'>--</span>
<a name="line-15"></a><span class='hs-comment'>-- Declaration of the MonadRWS class.</span>
<a name="line-16"></a><span class='hs-comment'>--</span>
<a name="line-17"></a><span class='hs-comment'>-- Inspired by the paper</span>
<a name="line-18"></a><span class='hs-comment'>-- /Functional Programming with Overloading and Higher-Order Polymorphism/,</span>
<a name="line-19"></a><span class='hs-comment'>-- Mark P Jones (<<a href="http://web.cecs.pdx.edu/~mpj/">http://web.cecs.pdx.edu/~mpj/</a>>)</span>
<a name="line-20"></a><span class='hs-comment'>-- Advanced School of Functional Programming, 1995.</span>
<a name="line-21"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-22"></a>
<a name="line-23"></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'>RWS</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span> <span class='hs-layout'>(</span>
<a name="line-24"></a> <span class='hs-conid'>MonadRWS</span><span class='hs-layout'>,</span>
<a name="line-25"></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-26"></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'>State</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span><span class='hs-layout'>,</span>
<a name="line-27"></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'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span><span class='hs-layout'>,</span>
<a name="line-28"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-29"></a>
<a name="line-30"></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'>Reader</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span>
<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'>State</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'>Writer</span><span class='hs-varop'>.</span><span class='hs-conid'>Class</span>
<a name="line-33"></a>
<a name="line-34"></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><span class='hs-layout'>(</span><span class='hs-conid'>Error</span><span class='hs-layout'>,</span> <span class='hs-conid'>ErrorT</span><span class='hs-layout'>)</span>
<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'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Maybe</span><span class='hs-layout'>(</span><span class='hs-conid'>MaybeT</span><span class='hs-layout'>)</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><span class='hs-varop'>.</span><span class='hs-conid'>Trans</span><span class='hs-varop'>.</span><span class='hs-conid'>Identity</span><span class='hs-layout'>(</span><span class='hs-conid'>IdentityT</span><span class='hs-layout'>)</span>
<a name="line-37"></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'>RWS</span><span class='hs-varop'>.</span><span class='hs-conid'>Lazy</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>Lazy</span> <span class='hs-layout'>(</span><span class='hs-conid'>RWST</span><span class='hs-layout'>)</span>
<a name="line-38"></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'>Strict</span> <span class='hs-layout'>(</span><span class='hs-conid'>RWST</span><span class='hs-layout'>)</span>
<a name="line-39"></a>
<a name="line-40"></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-41"></a>
<a name="line-42"></a><a name="MonadRWS"></a><span class='hs-keyword'>class</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-conid'>MonadWriter</span> <span class='hs-varid'>w</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>MonadState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span>
<a name="line-43"></a> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadRWS</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-keyglyph'>|</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>r</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>w</span><span class='hs-layout'>,</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>s</span>
<a name="line-44"></a>
<a name="line-45"></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'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadRWS</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>Lazy</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>
<a name="line-46"></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'>Monad</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadRWS</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>Strict</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>
<a name="line-47"></a>
<a name="line-48"></a><span class='hs-comment'>---------------------------------------------------------------------------</span>
<a name="line-49"></a><span class='hs-comment'>-- Instances for other mtl transformers</span>
<a name="line-50"></a><span class='hs-comment'>--</span>
<a name="line-51"></a><span class='hs-comment'>-- All of these instances need UndecidableInstances,</span>
<a name="line-52"></a><span class='hs-comment'>-- because they do not satisfy the coverage condition.</span>
<a name="line-53"></a>
<a name="line-54"></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'>MonadRWS</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-keyglyph'>=></span> <span class='hs-conid'>MonadRWS</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</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>
<a name="line-55"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadRWS</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-keyglyph'>=></span> <span class='hs-conid'>MonadRWS</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>IdentityT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span>
<a name="line-56"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadRWS</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-keyglyph'>=></span> <span class='hs-conid'>MonadRWS</span> <span class='hs-varid'>r</span> <span class='hs-varid'>w</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>MaybeT</span> <span class='hs-varid'>m</span><span class='hs-layout'>)</span>
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