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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE GeneralizedNewtypeDeriving #-}</span>
<a name="line-2"></a><span class='hs-comment'>{- |
<a name="line-3"></a>Module defining the type for exception free I/O.
<a name="line-4"></a>Exceptional results in SIO must be represented by traditional error codes.
<a name="line-5"></a>
<a name="line-6"></a>If you want to turn an IO action into 'SIO'
<a name="line-7"></a>you must convert it to @ExceptionalT IOException SIO a@
<a name="line-8"></a>by 'ioToExceptionalSIO' (or 'Control.Monad.Trans.liftIO')
<a name="line-9"></a>and then handle the 'IOException's using 'SyncExc.resolveT'.
<a name="line-10"></a>-}</span>
<a name="line-11"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Straight</span> <span class='hs-layout'>(</span>
<a name="line-12"></a> <span class='hs-conid'>SIO</span><span class='hs-layout'>,</span> <span class='hs-varid'>sioToIO</span><span class='hs-layout'>,</span> <span class='hs-varid'>ioToExceptionalSIO</span><span class='hs-layout'>,</span> <span class='hs-varid'>unsafeInterleaveSIO</span><span class='hs-layout'>,</span>
<a name="line-13"></a> <span class='hs-conid'>ExceptionalT</span><span class='hs-layout'>,</span> <span class='hs-conid'>IOException</span><span class='hs-layout'>,</span>
<a name="line-14"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-15"></a>
<a name="line-16"></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'>Exception</span><span class='hs-varop'>.</span><span class='hs-conid'>Synchronous</span>
<a name="line-17"></a> <span class='hs-layout'>(</span><span class='hs-conid'>Exceptional</span><span class='hs-layout'>(</span><span class='hs-conid'>Success</span><span class='hs-layout'>,</span> <span class='hs-conid'>Exception</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-conid'>ExceptionalT</span><span class='hs-layout'>(</span><span class='hs-conid'>ExceptionalT</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-layout'>)</span>
<a name="line-18"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Exception</span> <span class='hs-layout'>(</span><span class='hs-conid'>IOException</span><span class='hs-layout'>)</span>
<a name="line-19"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Error</span> <span class='hs-layout'>(</span><span class='hs-varid'>try</span><span class='hs-layout'>)</span>
<a name="line-20"></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> <span class='hs-layout'>(</span><span class='hs-conid'>MonadIO</span><span class='hs-layout'>,</span> <span class='hs-varid'>liftIO</span><span class='hs-layout'>,</span> <span class='hs-layout'>)</span>
<a name="line-21"></a>
<a name="line-22"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>System</span><span class='hs-varop'>.</span><span class='hs-conid'>IO</span><span class='hs-varop'>.</span><span class='hs-conid'>Unsafe</span> <span class='hs-layout'>(</span><span class='hs-varid'>unsafeInterleaveIO</span><span class='hs-layout'>,</span> <span class='hs-layout'>)</span>
<a name="line-23"></a>
<a name="line-24"></a>
<a name="line-25"></a><a name="SIO"></a><span class='hs-comment'>{- |
<a name="line-26"></a>An I/O action of type 'SIO' cannot skip following SIO actions
<a name="line-27"></a>as a result of exceptional outcomes like \"File not found\".
<a name="line-28"></a>However an 'error' can well break the program.
<a name="line-29"></a>-}</span>
<a name="line-30"></a><a name="SIO"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>SIO</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>SIO</span> <span class='hs-layout'>(</span><span class='hs-conid'>IO</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- {sioToIO :: IO a}</span>
<a name="line-31"></a> <span class='hs-keyword'>deriving</span> <span class='hs-layout'>(</span><span class='hs-conid'>Functor</span><span class='hs-layout'>,</span> <span class='hs-conid'>Monad</span><span class='hs-layout'>)</span>
<a name="line-32"></a>
<a name="line-33"></a>
<a name="line-34"></a><a name="sioToIO"></a><span class='hs-definition'>sioToIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SIO</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span>
<a name="line-35"></a><span class='hs-definition'>sioToIO</span> <span class='hs-layout'>(</span><span class='hs-conid'>SIO</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>x</span>
<a name="line-36"></a>
<a name="line-37"></a><a name="ioToExceptionalSIO"></a><span class='hs-definition'>ioToExceptionalSIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>ExceptionalT</span> <span class='hs-conid'>IOException</span> <span class='hs-conid'>SIO</span> <span class='hs-varid'>a</span>
<a name="line-38"></a><span class='hs-definition'>ioToExceptionalSIO</span> <span class='hs-keyglyph'>=</span>
<a name="line-39"></a> <span class='hs-conid'>ExceptionalT</span> <span class='hs-varop'>.</span> <span class='hs-conid'>SIO</span> <span class='hs-varop'>.</span> <span class='hs-varid'>fmap</span> <span class='hs-layout'>(</span><span class='hs-varid'>either</span> <span class='hs-conid'>Exception</span> <span class='hs-conid'>Success</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-varid'>try</span>
<a name="line-40"></a>
<a name="line-41"></a>
<a name="line-42"></a><a name="unsafeInterleaveSIO"></a><span class='hs-definition'>unsafeInterleaveSIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SIO</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>SIO</span> <span class='hs-varid'>a</span>
<a name="line-43"></a><span class='hs-definition'>unsafeInterleaveSIO</span> <span class='hs-layout'>(</span><span class='hs-conid'>SIO</span> <span class='hs-varid'>io</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>SIO</span> <span class='hs-varop'>$</span> <span class='hs-varid'>unsafeInterleaveIO</span> <span class='hs-varid'>io</span>
<a name="line-44"></a>
<a name="line-45"></a><span class='hs-comment'>-- helper classes for defining the MonadIO instance of SIO</span>
<a name="line-46"></a>
<a name="line-47"></a><a name="MonadSIO"></a><span class='hs-comment'>{- |
<a name="line-48"></a>Users of the library may define new instances of MonadSIO,
<a name="line-49"></a>but monads other than SIO may not make the absence of exceptions explicit.
<a name="line-50"></a>It is important however, that we do not make the method 'toSIO' public,
<a name="line-51"></a>since this would allow users
<a name="line-52"></a>the unsafe conversion from @IO@ to @SIO@.
<a name="line-53"></a>-}</span>
<a name="line-54"></a><a name="MonadSIO"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>Monad</span> <span class='hs-varid'>m</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>MonadSIO</span> <span class='hs-varid'>m</span> <span class='hs-keyword'>where</span> <span class='hs-varid'>toSIO</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IO</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>m</span> <span class='hs-varid'>a</span>
<a name="line-55"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>MonadSIO</span> <span class='hs-conid'>SIO</span> <span class='hs-keyword'>where</span> <span class='hs-varid'>toSIO</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>SIO</span>
<a name="line-56"></a>
<a name="line-57"></a><a name="ContainsIOException"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>ContainsIOException</span> <span class='hs-varid'>e</span> <span class='hs-keyword'>where</span> <span class='hs-varid'>fromIOException</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>IOException</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>e</span>
<a name="line-58"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ContainsIOException</span> <span class='hs-conid'>IOException</span> <span class='hs-keyword'>where</span> <span class='hs-varid'>fromIOException</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>id</span>
<a name="line-59"></a>
<a name="line-60"></a>
<a name="line-61"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>MonadSIO</span> <span class='hs-varid'>m</span><span class='hs-layout'>,</span> <span class='hs-conid'>ContainsIOException</span> <span class='hs-varid'>e</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span>
<a name="line-62"></a> <span class='hs-conid'>MonadIO</span> <span class='hs-layout'>(</span><span class='hs-conid'>ExceptionalT</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-63"></a> <span class='hs-varid'>liftIO</span> <span class='hs-keyglyph'>=</span>
<a name="line-64"></a> <span class='hs-conid'>ExceptionalT</span> <span class='hs-varop'>.</span> <span class='hs-varid'>toSIO</span> <span class='hs-varop'>.</span>
<a name="line-65"></a> <span class='hs-varid'>fmap</span> <span class='hs-layout'>(</span><span class='hs-varid'>either</span> <span class='hs-layout'>(</span><span class='hs-conid'>Exception</span> <span class='hs-varop'>.</span> <span class='hs-varid'>fromIOException</span><span class='hs-layout'>)</span> <span class='hs-conid'>Success</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-varid'>try</span>
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