<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head> <!-- Generated by HsColour, http://code.haskell.org/~malcolm/hscolour/ --> <title>Control/Arrow/Internals.hs</title> <link type='text/css' rel='stylesheet' href='hscolour.css' /> </head> <body> <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.Arrow.Internals</span> <a name="line-4"></a><span class='hs-comment'>-- Copyright : (c) Ross Paterson 2003</span> <a name="line-5"></a><span class='hs-comment'>-- License : BSD-style (see the LICENSE file in the distribution)</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 : non-portable (multi-parameter type classes)</span> <a name="line-10"></a><span class='hs-comment'>--</span> <a name="line-11"></a><span class='hs-comment'>-- Manipulation of composite arrow types, beyond the basic lifting and</span> <a name="line-12"></a><span class='hs-comment'>-- encapsulation provided with each arrow transformer.</span> <a name="line-13"></a><span class='hs-comment'>--</span> <a name="line-14"></a><span class='hs-comment'>-- The signatures are designed to be compatible with the proposed notation</span> <a name="line-15"></a><span class='hs-comment'>-- for arrows, cf. <<a href="http://www.haskell.org/arrows/">http://www.haskell.org/arrows/</a>>.</span> <a name="line-16"></a> <a name="line-17"></a><span class='hs-comment'>-- #hide</span> <a name="line-18"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Arrow</span><span class='hs-varop'>.</span><span class='hs-conid'>Internals</span> <span class='hs-layout'>(</span> <a name="line-19"></a> <span class='hs-conid'>ArrowAddState</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <a name="line-20"></a> <span class='hs-conid'>ArrowAddReader</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <a name="line-21"></a> <span class='hs-conid'>ArrowAddWriter</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <a name="line-22"></a> <span class='hs-conid'>ArrowAddError</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <a name="line-23"></a> <span class='hs-conid'>ArrowAddStream</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-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-25"></a> <a name="line-26"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Arrow</span> <a name="line-27"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Arrow</span><span class='hs-varop'>.</span><span class='hs-conid'>Operations</span> <a name="line-28"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Stream</span> <a name="line-29"></a> <a name="line-30"></a><span class='hs-comment'>-- | Adding a 'Control.Arrow.Transformer.State.StateArrow' to an</span> <a name="line-31"></a><span class='hs-comment'>-- arrow type, but not necessarily as the outer arrow transformer.</span> <a name="line-32"></a><span class='hs-comment'>--</span> <a name="line-33"></a><span class='hs-comment'>-- Typically a composite arrow type is built by applying a series</span> <a name="line-34"></a><span class='hs-comment'>-- of arrow transformer to a base arrow (usually either a function</span> <a name="line-35"></a><span class='hs-comment'>-- arrow or a 'Kleisli' arrow. One can add a transformer to the</span> <a name="line-36"></a><span class='hs-comment'>-- top of this stack using the 'Control.Arrow.Transformer.lift'</span> <a name="line-37"></a><span class='hs-comment'>-- method of the 'Control.Arrow.Transformer.ArrowTransformer' class,</span> <a name="line-38"></a><span class='hs-comment'>-- or remove a state transformer from the top of the stack using the</span> <a name="line-39"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.State.runState' encapsulation operator.</span> <a name="line-40"></a><span class='hs-comment'>-- The methods of this class add and remove state transformers anywhere</span> <a name="line-41"></a><span class='hs-comment'>-- in the stack. In the instance</span> <a name="line-42"></a><span class='hs-comment'>--</span> <a name="line-43"></a><span class='hs-comment'>-- > instance Arrow a => ArrowAddState s (ArrowState s a) a</span> <a name="line-44"></a><span class='hs-comment'>--</span> <a name="line-45"></a><span class='hs-comment'>-- they are equivalent to 'Control.Arrow.Transformer.lift' and</span> <a name="line-46"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.State.runState' respectively.</span> <a name="line-47"></a><span class='hs-comment'>-- Instances are lifted through other transformers with</span> <a name="line-48"></a><span class='hs-comment'>--</span> <a name="line-49"></a><span class='hs-comment'>-- > instance ArrowAddState s a a' =></span> <a name="line-50"></a><span class='hs-comment'>-- > ArrowAddState s (FooArrow a) (FooArrow a')</span> <a name="line-51"></a> <a name="line-52"></a><a name="ArrowAddState"></a><span class='hs-keyword'>class</span> <span class='hs-layout'>(</span><span class='hs-conid'>ArrowState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>Arrow</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowAddState</span> <span class='hs-varid'>s</span> <span class='hs-varid'>a</span> <span class='hs-varid'>a'</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-keyword'>where</span> <a name="line-53"></a> <a name="line-54"></a> <span class='hs-comment'>-- | Lift a computation from an arrow to one with an added state.</span> <a name="line-55"></a> <span class='hs-comment'>--</span> <a name="line-56"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-57"></a> <span class='hs-comment'>--</span> <a name="line-58"></a> <span class='hs-comment'>-- > proc p -> ...</span> <a name="line-59"></a> <span class='hs-comment'>-- > (|liftState cmd|)</span> <a name="line-60"></a> <a name="line-61"></a> <span class='hs-varid'>liftState</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a'</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <a name="line-62"></a> <a name="line-63"></a> <span class='hs-comment'>-- | Elimination of a state transformer from a computation,</span> <a name="line-64"></a> <span class='hs-comment'>-- exposing the initial and final states.</span> <a name="line-65"></a> <span class='hs-comment'>--</span> <a name="line-66"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-67"></a> <span class='hs-comment'>--</span> <a name="line-68"></a> <span class='hs-comment'>-- > proc p -> do</span> <a name="line-69"></a> <span class='hs-comment'>-- > ...</span> <a name="line-70"></a> <span class='hs-comment'>-- > (result, final_state) <- (|elimState cmd|) init_state</span> <a name="line-71"></a> <a name="line-72"></a> <span class='hs-varid'>elimState</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span><span class='hs-layout'>,</span><span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>b</span><span class='hs-layout'>,</span><span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-73"></a> <a name="line-74"></a><span class='hs-comment'>-- | Adding a 'Control.Arrow.Transformer.Reader.ReaderArrow' to an</span> <a name="line-75"></a><span class='hs-comment'>-- arrow type, but not necessarily as the outer arrow transformer.</span> <a name="line-76"></a><span class='hs-comment'>--</span> <a name="line-77"></a><span class='hs-comment'>-- Typically a composite arrow type is built by applying a series</span> <a name="line-78"></a><span class='hs-comment'>-- of arrow transformer to a base arrow (usually either a function</span> <a name="line-79"></a><span class='hs-comment'>-- arrow or a 'Kleisli' arrow. One can add a transformer to the</span> <a name="line-80"></a><span class='hs-comment'>-- top of this stack using the 'Control.Arrow.Transformer.lift'</span> <a name="line-81"></a><span class='hs-comment'>-- method of the 'Control.Arrow.Transformer.ArrowTransformer' class,</span> <a name="line-82"></a><span class='hs-comment'>-- or remove a state transformer from the top of the stack using the</span> <a name="line-83"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Reader.runReader' encapsulation operator.</span> <a name="line-84"></a><span class='hs-comment'>-- The methods of this class add and remove state transformers anywhere</span> <a name="line-85"></a><span class='hs-comment'>-- in the stack. In the instance</span> <a name="line-86"></a><span class='hs-comment'>--</span> <a name="line-87"></a><span class='hs-comment'>-- > instance Arrow a => ArrowAddReader r (ArrowReader r a) a</span> <a name="line-88"></a><span class='hs-comment'>--</span> <a name="line-89"></a><span class='hs-comment'>-- they are equivalent to 'Control.Arrow.Transformer.lift' and</span> <a name="line-90"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Reader.runReader' respectively.</span> <a name="line-91"></a><span class='hs-comment'>-- Instances are lifted through other transformers with</span> <a name="line-92"></a><span class='hs-comment'>--</span> <a name="line-93"></a><span class='hs-comment'>-- > instance ArrowAddReader r a a' =></span> <a name="line-94"></a><span class='hs-comment'>-- > ArrowAddReader r (FooArrow a) (FooArrow a')</span> <a name="line-95"></a> <a name="line-96"></a><a name="ArrowAddReader"></a><span class='hs-keyword'>class</span> <span class='hs-layout'>(</span><span class='hs-conid'>ArrowReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>Arrow</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowAddReader</span> <span class='hs-varid'>r</span> <span class='hs-varid'>a</span> <span class='hs-varid'>a'</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-keyword'>where</span> <a name="line-97"></a> <a name="line-98"></a> <span class='hs-comment'>-- | Lift a computation from an arrow to one with an added environment.</span> <a name="line-99"></a> <span class='hs-comment'>--</span> <a name="line-100"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-101"></a> <span class='hs-comment'>--</span> <a name="line-102"></a> <span class='hs-comment'>-- > proc p -> ...</span> <a name="line-103"></a> <span class='hs-comment'>-- > (|liftReader cmd|)</span> <a name="line-104"></a> <a name="line-105"></a> <span class='hs-varid'>liftReader</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a'</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <a name="line-106"></a> <a name="line-107"></a> <span class='hs-comment'>-- | Elimination of a state reader from a computation,</span> <a name="line-108"></a> <span class='hs-comment'>-- taking a value for the state.</span> <a name="line-109"></a> <span class='hs-comment'>--</span> <a name="line-110"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-111"></a> <span class='hs-comment'>--</span> <a name="line-112"></a> <span class='hs-comment'>-- > proc p -> ...</span> <a name="line-113"></a> <span class='hs-comment'>-- > (|elimReader cmd|) env</span> <a name="line-114"></a> <a name="line-115"></a> <span class='hs-varid'>elimReader</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span><span class='hs-layout'>,</span><span class='hs-varid'>r</span><span class='hs-layout'>)</span> <span class='hs-varid'>b</span> <a name="line-116"></a> <a name="line-117"></a><span class='hs-comment'>-- | Adding a 'Control.Arrow.Transformer.Writer.WriterArrow' to an</span> <a name="line-118"></a><span class='hs-comment'>-- arrow type, but not necessarily as the outer arrow transformer.</span> <a name="line-119"></a><span class='hs-comment'>--</span> <a name="line-120"></a><span class='hs-comment'>-- Typically a composite arrow type is built by applying a series</span> <a name="line-121"></a><span class='hs-comment'>-- of arrow transformer to a base arrow (usually either a function</span> <a name="line-122"></a><span class='hs-comment'>-- arrow or a 'Kleisli' arrow. One can add a transformer to the</span> <a name="line-123"></a><span class='hs-comment'>-- top of this stack using the 'Control.Arrow.Transformer.lift'</span> <a name="line-124"></a><span class='hs-comment'>-- method of the 'Control.Arrow.Transformer.ArrowTransformer' class,</span> <a name="line-125"></a><span class='hs-comment'>-- or remove a state transformer from the top of the stack using the</span> <a name="line-126"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Writer.runWriter' encapsulation operator.</span> <a name="line-127"></a><span class='hs-comment'>-- The methods of this class add and remove state transformers anywhere</span> <a name="line-128"></a><span class='hs-comment'>-- in the stack. In the instance</span> <a name="line-129"></a><span class='hs-comment'>--</span> <a name="line-130"></a><span class='hs-comment'>-- > instance Arrow a => ArrowAddWriter w (ArrowWriter w a) a</span> <a name="line-131"></a><span class='hs-comment'>--</span> <a name="line-132"></a><span class='hs-comment'>-- they are equivalent to 'Control.Arrow.Transformer.lift' and</span> <a name="line-133"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Writer.runWriter' respectively.</span> <a name="line-134"></a><span class='hs-comment'>-- Instances are lifted through other transformers with</span> <a name="line-135"></a><span class='hs-comment'>--</span> <a name="line-136"></a><span class='hs-comment'>-- > instance ArrowAddWriter w a a' =></span> <a name="line-137"></a><span class='hs-comment'>-- > ArrowAddWriter w (FooArrow a) (FooArrow a')</span> <a name="line-138"></a> <a name="line-139"></a><a name="ArrowAddWriter"></a><span class='hs-keyword'>class</span> <span class='hs-layout'>(</span><span class='hs-conid'>ArrowWriter</span> <span class='hs-varid'>w</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>Arrow</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowAddWriter</span> <span class='hs-varid'>w</span> <span class='hs-varid'>a</span> <span class='hs-varid'>a'</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-keyword'>where</span> <a name="line-140"></a> <a name="line-141"></a> <span class='hs-comment'>-- | Lift a computation from an arrow to one with added output.</span> <a name="line-142"></a> <span class='hs-comment'>--</span> <a name="line-143"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-144"></a> <span class='hs-comment'>--</span> <a name="line-145"></a> <span class='hs-comment'>-- > proc p -> ...</span> <a name="line-146"></a> <span class='hs-comment'>-- > (|liftWriter cmd|)</span> <a name="line-147"></a> <a name="line-148"></a> <span class='hs-varid'>liftWriter</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a'</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <a name="line-149"></a> <a name="line-150"></a> <span class='hs-comment'>-- | Elimination of an output writer from a computation,</span> <a name="line-151"></a> <span class='hs-comment'>-- providing the accumulated output.</span> <a name="line-152"></a> <span class='hs-comment'>--</span> <a name="line-153"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-154"></a> <span class='hs-comment'>--</span> <a name="line-155"></a> <span class='hs-comment'>-- > proc p -> do</span> <a name="line-156"></a> <span class='hs-comment'>-- > ...</span> <a name="line-157"></a> <span class='hs-comment'>-- > (result, output) <- (|elimWriter cmd|)</span> <a name="line-158"></a> <a name="line-159"></a> <span class='hs-varid'>elimWriter</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-varid'>e</span> <span class='hs-layout'>(</span><span class='hs-varid'>b</span><span class='hs-layout'>,</span><span class='hs-varid'>w</span><span class='hs-layout'>)</span> <a name="line-160"></a> <a name="line-161"></a><span class='hs-comment'>-- | Adding a 'Control.Arrow.Transformer.Error.ErrorArrow' to an</span> <a name="line-162"></a><span class='hs-comment'>-- arrow type, but not necessarily as the outer arrow transformer.</span> <a name="line-163"></a><span class='hs-comment'>--</span> <a name="line-164"></a><span class='hs-comment'>-- Typically a composite arrow type is built by applying a series</span> <a name="line-165"></a><span class='hs-comment'>-- of arrow transformer to a base arrow (usually either a function</span> <a name="line-166"></a><span class='hs-comment'>-- arrow or a 'Kleisli' arrow. One can add a transformer to the</span> <a name="line-167"></a><span class='hs-comment'>-- top of this stack using the 'Control.Arrow.Transformer.lift'</span> <a name="line-168"></a><span class='hs-comment'>-- method of the 'Control.Arrow.Transformer.ArrowTransformer' class,</span> <a name="line-169"></a><span class='hs-comment'>-- or remove a state transformer from the top of the stack using the</span> <a name="line-170"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Error.runError' encapsulation operator.</span> <a name="line-171"></a><span class='hs-comment'>-- The methods of this class add and remove state transformers anywhere</span> <a name="line-172"></a><span class='hs-comment'>-- in the stack. In the instance</span> <a name="line-173"></a><span class='hs-comment'>--</span> <a name="line-174"></a><span class='hs-comment'>-- > instance Arrow a => ArrowAddError ex (ArrowError ex a) a</span> <a name="line-175"></a><span class='hs-comment'>--</span> <a name="line-176"></a><span class='hs-comment'>-- they are equivalent to 'Control.Arrow.Transformer.lift' and</span> <a name="line-177"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Error.runError' respectively.</span> <a name="line-178"></a><span class='hs-comment'>-- Instances are lifted through other transformers with</span> <a name="line-179"></a><span class='hs-comment'>--</span> <a name="line-180"></a><span class='hs-comment'>-- > instance ArrowAddError ex a a' =></span> <a name="line-181"></a><span class='hs-comment'>-- > ArrowAddError ex (FooArrow a) (FooArrow a')</span> <a name="line-182"></a><span class='hs-comment'>--</span> <a name="line-183"></a><span class='hs-comment'>-- This could be combined with 'Control.Arrow.Transformer.Error.handle',</span> <a name="line-184"></a><span class='hs-comment'>-- since the resulting arrow is always the arrow of the handler.</span> <a name="line-185"></a><span class='hs-comment'>-- Separating them has the advantage of consistency with the other arrows,</span> <a name="line-186"></a><span class='hs-comment'>-- and might give more helpful type error messages.</span> <a name="line-187"></a> <a name="line-188"></a><a name="ArrowAddError"></a><span class='hs-keyword'>class</span> <span class='hs-layout'>(</span><span class='hs-conid'>ArrowError</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>Arrow</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowAddError</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span> <span class='hs-varid'>a'</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-keyword'>where</span> <a name="line-189"></a> <a name="line-190"></a> <span class='hs-comment'>-- | Lift a computation from an arrow to one with error handling.</span> <a name="line-191"></a> <span class='hs-comment'>--</span> <a name="line-192"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-193"></a> <span class='hs-comment'>--</span> <a name="line-194"></a> <span class='hs-comment'>-- > proc p -> ...</span> <a name="line-195"></a> <span class='hs-comment'>-- > (|liftError cmd|)</span> <a name="line-196"></a> <a name="line-197"></a> <span class='hs-varid'>liftError</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a'</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <a name="line-198"></a> <a name="line-199"></a> <span class='hs-comment'>-- | Elimination of errors from a computation,</span> <a name="line-200"></a> <span class='hs-comment'>-- by completely handling any errors.</span> <a name="line-201"></a> <span class='hs-comment'>--</span> <a name="line-202"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-203"></a> <span class='hs-comment'>--</span> <a name="line-204"></a> <span class='hs-comment'>-- > proc p -> ...</span> <a name="line-205"></a> <span class='hs-comment'>-- > body `elimError` \ex -> handler</span> <a name="line-206"></a> <a name="line-207"></a> <span class='hs-varid'>elimError</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span><span class='hs-layout'>,</span><span class='hs-varid'>ex</span><span class='hs-layout'>)</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <a name="line-208"></a> <a name="line-209"></a><span class='hs-comment'>-- | Adding a 'Control.Arrow.Transformer.Stream.StreamArrow' to an</span> <a name="line-210"></a><span class='hs-comment'>-- arrow type, but not necessarily as the outer arrow transformer.</span> <a name="line-211"></a><span class='hs-comment'>--</span> <a name="line-212"></a><span class='hs-comment'>-- Typically a composite arrow type is built by applying a series</span> <a name="line-213"></a><span class='hs-comment'>-- of arrow transformer to a base arrow (usually either a function</span> <a name="line-214"></a><span class='hs-comment'>-- arrow or a 'Kleisli' arrow. One can add a transformer to the</span> <a name="line-215"></a><span class='hs-comment'>-- top of this stack using the 'Control.Arrow.Transformer.lift'</span> <a name="line-216"></a><span class='hs-comment'>-- method of the 'Control.Arrow.Transformer.ArrowTransformer' class,</span> <a name="line-217"></a><span class='hs-comment'>-- or remove a state transformer from the top of the stack using the</span> <a name="line-218"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Stream.runStream' encapsulation operator.</span> <a name="line-219"></a><span class='hs-comment'>-- The methods of this class add and remove state transformers anywhere</span> <a name="line-220"></a><span class='hs-comment'>-- in the stack. In the instance</span> <a name="line-221"></a><span class='hs-comment'>--</span> <a name="line-222"></a><span class='hs-comment'>-- > instance Arrow a => ArrowAddStream (ArrowStream a) a</span> <a name="line-223"></a><span class='hs-comment'>--</span> <a name="line-224"></a><span class='hs-comment'>-- they are equivalent to 'Control.Arrow.Transformer.lift' and</span> <a name="line-225"></a><span class='hs-comment'>-- 'Control.Arrow.Transformer.Stream.runStream' respectively.</span> <a name="line-226"></a><span class='hs-comment'>-- Instances are lifted through other transformers with</span> <a name="line-227"></a><span class='hs-comment'>--</span> <a name="line-228"></a><span class='hs-comment'>-- > instance ArrowAddStream a a' =></span> <a name="line-229"></a><span class='hs-comment'>-- > ArrowAddStream (FooArrow a) (FooArrow a')</span> <a name="line-230"></a> <a name="line-231"></a><a name="ArrowAddStream"></a><span class='hs-keyword'>class</span> <span class='hs-layout'>(</span><span class='hs-conid'>ArrowCircuit</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>Arrow</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowAddStream</span> <span class='hs-varid'>a</span> <span class='hs-varid'>a'</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-keyword'>where</span> <a name="line-232"></a> <a name="line-233"></a> <span class='hs-comment'>-- | Lift a computation from an arrow to a stream processing one.</span> <a name="line-234"></a> <span class='hs-comment'>--</span> <a name="line-235"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-236"></a> <span class='hs-comment'>--</span> <a name="line-237"></a> <span class='hs-comment'>-- > proc p -> ...</span> <a name="line-238"></a> <span class='hs-comment'>-- > (|liftStream cmd|)</span> <a name="line-239"></a> <a name="line-240"></a> <span class='hs-varid'>liftStream</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a'</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <a name="line-241"></a> <a name="line-242"></a> <span class='hs-comment'>-- | Run a stream processor on a stream of inputs,</span> <a name="line-243"></a> <span class='hs-comment'>-- obtaining a stream of outputs.</span> <a name="line-244"></a> <span class='hs-comment'>--</span> <a name="line-245"></a> <span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-246"></a> <span class='hs-comment'>--</span> <a name="line-247"></a> <span class='hs-comment'>-- > proc p -> do</span> <a name="line-248"></a> <span class='hs-comment'>-- > ...</span> <a name="line-249"></a> <span class='hs-comment'>-- > ys <- (|elimStream (\x -> ...)|) xs</span> <a name="line-250"></a> <span class='hs-comment'>--</span> <a name="line-251"></a> <span class='hs-comment'>-- Here @xs@ refers to the input stream and @x@ to individual</span> <a name="line-252"></a> <span class='hs-comment'>-- elements of that stream. @ys@ is bound to the output stream.</span> <a name="line-253"></a> <a name="line-254"></a> <span class='hs-varid'>elimStream</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>a</span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span><span class='hs-layout'>,</span><span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-varid'>c</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a'</span> <span class='hs-layout'>(</span><span class='hs-varid'>e</span><span class='hs-layout'>,</span><span class='hs-conid'>Stream</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>Stream</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> </pre></body> </html>
distrib
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Fedora
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18
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x86_64
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media
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updates
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by-pkgid
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765adc18ec52512b3512a9992c59746e
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files
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79
