<?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/Transformer/Error.hs</title> <link type='text/css' rel='stylesheet' href='hscolour.css' /> </head> <body> <pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE FlexibleInstances #-}</span> <a name="line-2"></a> <a name="line-3"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span> <a name="line-4"></a><span class='hs-comment'>-- |</span> <a name="line-5"></a><span class='hs-comment'>-- Module : Control.Arrow.Transformer.Error</span> <a name="line-6"></a><span class='hs-comment'>-- Copyright : (c) Ross Paterson 2003</span> <a name="line-7"></a><span class='hs-comment'>-- License : BSD-style (see the LICENSE file in the distribution)</span> <a name="line-8"></a><span class='hs-comment'>--</span> <a name="line-9"></a><span class='hs-comment'>-- Maintainer : ross@soi.city.ac.uk</span> <a name="line-10"></a><span class='hs-comment'>-- Stability : experimental</span> <a name="line-11"></a><span class='hs-comment'>-- Portability : non-portable (multi-parameter type classes)</span> <a name="line-12"></a><span class='hs-comment'>--</span> <a name="line-13"></a><span class='hs-comment'>-- An arrow transformer that adds error handling.</span> <a name="line-14"></a><span class='hs-comment'>--</span> <a name="line-15"></a><span class='hs-comment'>-- /TODO:/ the operations here are inconsistent with other arrow transformers.</span> <a name="line-16"></a> <a name="line-17"></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'>Transformer</span><span class='hs-varop'>.</span><span class='hs-conid'>Error</span><span class='hs-layout'>(</span> <a name="line-18"></a> <span class='hs-conid'>ErrorArrow</span><span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <a name="line-19"></a> <span class='hs-varid'>runError</span><span class='hs-layout'>,</span> <a name="line-20"></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-21"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-22"></a> <a name="line-23"></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'>Internals</span> <a name="line-24"></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-25"></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'>Transformer</span> <a name="line-26"></a> <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'>Applicative</span> <a name="line-28"></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-29"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Category</span> <a name="line-30"></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-31"></a> <a name="line-32"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Prelude</span> <span class='hs-varid'>hiding</span> <span class='hs-layout'>(</span><span class='hs-varid'>id</span><span class='hs-layout'>,</span><span class='hs-layout'>(</span><span class='hs-varop'>.</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-33"></a> <a name="line-34"></a><span class='hs-comment'>-- | An arrow that augments an existing arrow with possible errors.</span> <a name="line-35"></a><span class='hs-comment'>-- The 'ArrowError' class contains methods for raising and handling</span> <a name="line-36"></a><span class='hs-comment'>-- these errors.</span> <a name="line-37"></a> <a name="line-38"></a><a name="ErrorArrow"></a><span class='hs-keyword'>newtype</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span> <span class='hs-varid'>c</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varid'>b</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-39"></a> <a name="line-40"></a><a name="rstrength"></a><span class='hs-definition'>rstrength</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Either</span> <span class='hs-varid'>ex</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <a name="line-41"></a><span class='hs-definition'>rstrength</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varid'>ex</span><span class='hs-layout'>,</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Left</span> <span class='hs-varid'>ex</span> <a name="line-42"></a><span class='hs-definition'>rstrength</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <a name="line-43"></a> <a name="line-44"></a><span class='hs-comment'>-- | Encapsulate an error-raising computation,</span> <a name="line-45"></a><span class='hs-comment'>-- by completely handling any errors.</span> <a name="line-46"></a><span class='hs-comment'>--</span> <a name="line-47"></a><span class='hs-comment'>-- Typical usage in arrow notation:</span> <a name="line-48"></a><span class='hs-comment'>--</span> <a name="line-49"></a><span class='hs-comment'>-- > proc p -> ...</span> <a name="line-50"></a><span class='hs-comment'>-- > body `runError` \ex -> handler</span> <a name="line-51"></a> <a name="line-52"></a><a name="runError"></a><span class='hs-definition'>runError</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <a name="line-53"></a> <span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span> <span class='hs-varid'>e</span> <span class='hs-varid'>b</span> <span class='hs-comment'>-- ^ computation that may raise errors</span> <a name="line-54"></a> <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-comment'>-- ^ computation to handle errors</span> <a name="line-55"></a> <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-56"></a><span class='hs-definition'>runError</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-varid'>h</span> <span class='hs-keyglyph'>=</span> <a name="line-57"></a> <span class='hs-varid'>arr</span> <span class='hs-varid'>id</span> <span class='hs-varop'>&&&</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>strength</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>h</span> <span class='hs-varop'>|||</span> <span class='hs-varid'>arr</span> <span class='hs-varid'>id</span> <a name="line-58"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>strength</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span> <span class='hs-conid'>Left</span> <span class='hs-varid'>y</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Left</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span> <span class='hs-varid'>y</span><span class='hs-layout'>)</span> <a name="line-59"></a> <span class='hs-varid'>strength</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-layout'>,</span> <span class='hs-conid'>Right</span> <span class='hs-varid'>z</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</span> <span class='hs-varid'>z</span> <a name="line-60"></a> <a name="line-61"></a><span class='hs-comment'>-- transformer</span> <a name="line-62"></a> <a name="line-63"></a><a name="instance%20ArrowTransformer%20(ErrorArrow%20ex)%20a"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowTransformer</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span> <span class='hs-keyword'>where</span> <a name="line-64"></a> <span class='hs-varid'>lift</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-conid'>Right</span><span class='hs-layout'>)</span> <a name="line-65"></a> <a name="line-66"></a><span class='hs-comment'>-- liftings of standard classes</span> <a name="line-67"></a> <a name="line-68"></a><a name="instance%20Category%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Category</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-69"></a> <span class='hs-varid'>id</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-conid'>Right</span><span class='hs-layout'>)</span> <a name="line-70"></a> <span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span> <span class='hs-varop'>.</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <a name="line-71"></a> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-layout'>(</span><span class='hs-varid'>either</span> <span class='hs-conid'>Left</span> <span class='hs-varid'>id</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-varid'>right</span> <span class='hs-varid'>f</span> <span class='hs-varop'>.</span> <span class='hs-varid'>g</span><span class='hs-layout'>)</span> <a name="line-72"></a> <a name="line-73"></a><a name="instance%20Arrow%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Arrow</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-74"></a> <span class='hs-varid'>arr</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-75"></a> <span class='hs-varid'>first</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>first</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>rstrength</span><span class='hs-layout'>)</span> <a name="line-76"></a> <a name="line-77"></a><a name="instance%20ArrowChoice%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-78"></a> <span class='hs-varid'>left</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>left</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>assocsum</span><span class='hs-layout'>)</span> <a name="line-79"></a> <a name="line-80"></a><a name="assocsum"></a><span class='hs-definition'>assocsum</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Either</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-varid'>a</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-conid'>Either</span> <span class='hs-varid'>a</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-varid'>b</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <a name="line-81"></a><span class='hs-definition'>assocsum</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Left</span> <span class='hs-varid'>a</span> <a name="line-82"></a><span class='hs-definition'>assocsum</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <a name="line-83"></a><span class='hs-definition'>assocsum</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <a name="line-84"></a> <a name="line-85"></a><a name="instance%20ArrowApply%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowApply</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowApply</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-86"></a> <span class='hs-varid'>app</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>,</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span><span class='hs-layout'>,</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>app</span><span class='hs-layout'>)</span> <a name="line-87"></a> <a name="line-88"></a><span class='hs-comment'>-- this instance has the right type, but it doesn't satisfy right</span> <a name="line-89"></a><span class='hs-comment'>-- tightening, or sliding of non-strict functions.</span> <a name="line-90"></a> <a name="line-91"></a><a name="instance%20ArrowLoop%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowLoop</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowLoop</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-92"></a> <span class='hs-varid'>loop</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>loop</span> <span class='hs-layout'>(</span><span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>dist</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-93"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>dist</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-layout'>(</span><span class='hs-varid'>fstRight</span> <span class='hs-varid'>x</span><span class='hs-layout'>,</span> <span class='hs-varid'>snd</span> <span class='hs-varop'>$</span> <span class='hs-varid'>fromRight</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <a name="line-94"></a> <span class='hs-varid'>fstRight</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Left</span> <span class='hs-varid'>x</span> <a name="line-95"></a> <span class='hs-varid'>fstRight</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span><span class='hs-keyword'>_</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</span> <span class='hs-varid'>x</span> <a name="line-96"></a> <span class='hs-varid'>fromRight</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>error</span> <span class='hs-str'>"fromRight"</span> <a name="line-97"></a> <span class='hs-varid'>fromRight</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-varid'>y</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>y</span> <a name="line-98"></a> <a name="line-99"></a><span class='hs-comment'>-- Other instances</span> <a name="line-100"></a> <a name="line-101"></a><a name="instance%20Functor%20(ErrorArrow%20ex%20a%20b)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Functor</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-102"></a> <span class='hs-varid'>fmap</span> <span class='hs-varid'>f</span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>g</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>f</span> <a name="line-103"></a> <a name="line-104"></a><a name="instance%20Applicative%20(ErrorArrow%20ex%20a%20b)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Applicative</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-105"></a> <span class='hs-varid'>pure</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>arr</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <a name="line-106"></a> <span class='hs-varid'>f</span> <span class='hs-varop'><*></span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-varop'>&&&</span> <span class='hs-varid'>g</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-layout'>(</span><span class='hs-varid'>uncurry</span> <span class='hs-varid'>id</span><span class='hs-layout'>)</span> <a name="line-107"></a> <a name="line-108"></a><a name="instance%20Alternative%20(ErrorArrow%20ex%20a%20b)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>ex</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Alternative</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-109"></a> <span class='hs-varid'>empty</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>zeroArrow</span> <a name="line-110"></a> <span class='hs-varid'>f</span> <span class='hs-varop'><|></span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-varop'><+></span> <span class='hs-varid'>g</span> <a name="line-111"></a> <a name="line-112"></a><a name="instance%20Monoid%20(ErrorArrow%20ex%20a%20b%20c)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>ex</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>Monoid</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-113"></a> <span class='hs-varid'>mempty</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>zeroArrow</span> <a name="line-114"></a> <span class='hs-varid'>mappend</span> <span class='hs-varid'>f</span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-varop'><+></span> <span class='hs-varid'>g</span> <a name="line-115"></a> <a name="line-116"></a><span class='hs-comment'>-- fresh instances</span> <a name="line-117"></a> <a name="line-118"></a><a name="instance%20ArrowError%20ex%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowError</span> <span class='hs-varid'>ex</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-119"></a> <span class='hs-varid'>raise</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-conid'>Left</span><span class='hs-layout'>)</span> <a name="line-120"></a> <span class='hs-varid'>handle</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>h</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <a name="line-121"></a> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-varid'>id</span> <span class='hs-varop'>&&&</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>strength</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>h</span> <span class='hs-varop'>|||</span> <span class='hs-varid'>arr</span> <span class='hs-conid'>Right</span><span class='hs-layout'>)</span> <a name="line-122"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>strength</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span> <span class='hs-conid'>Left</span> <span class='hs-varid'>y</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Left</span> <span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span> <span class='hs-varid'>y</span><span class='hs-layout'>)</span> <a name="line-123"></a> <span class='hs-varid'>strength</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-layout'>,</span> <span class='hs-conid'>Right</span> <span class='hs-varid'>z</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</span> <span class='hs-varid'>z</span> <a name="line-124"></a> <span class='hs-varid'>tryInUnless</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>h</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <a name="line-125"></a> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-varid'>id</span> <span class='hs-varop'>&&&</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>distr</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>h</span> <span class='hs-varop'>|||</span> <span class='hs-varid'>s</span><span class='hs-layout'>)</span> <a name="line-126"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>distr</span> <span class='hs-layout'>(</span><span class='hs-varid'>b</span><span class='hs-layout'>,</span> <span class='hs-conid'>Left</span> <span class='hs-varid'>ex</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Left</span> <span class='hs-layout'>(</span><span class='hs-varid'>b</span><span class='hs-layout'>,</span> <span class='hs-varid'>ex</span><span class='hs-layout'>)</span> <a name="line-127"></a> <span class='hs-varid'>distr</span> <span class='hs-layout'>(</span><span class='hs-varid'>b</span><span class='hs-layout'>,</span> <span class='hs-conid'>Right</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Right</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-layout'>)</span> <a name="line-128"></a> <a name="line-129"></a><a name="instance%20ArrowAddError%20ex%20(ErrorArrow%20ex%20a)%20a"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowAddError</span> <span class='hs-varid'>ex</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-varid'>a</span> <span class='hs-keyword'>where</span> <a name="line-130"></a> <span class='hs-varid'>liftError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <a name="line-131"></a> <span class='hs-varid'>elimError</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>runError</span> <a name="line-132"></a> <a name="line-133"></a><a name="instance%20ArrowZero%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>ex</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowZero</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-134"></a> <span class='hs-varid'>zeroArrow</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varid'>mempty</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-135"></a> <a name="line-136"></a><a name="instance%20ArrowPlus%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</span><span class='hs-conid'>Monoid</span> <span class='hs-varid'>ex</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowPlus</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-137"></a> <span class='hs-varid'>f</span> <span class='hs-varop'><+></span> <span class='hs-varid'>g</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>handle</span> <span class='hs-varid'>f</span> <span class='hs-varop'>$</span> <span class='hs-varid'>handle</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-varid'>fst</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>g</span><span class='hs-layout'>)</span> <span class='hs-varop'>$</span> <a name="line-138"></a> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>arr</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-layout'>,</span><span class='hs-varid'>ex1</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>ex2</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <a name="line-139"></a> <span class='hs-conid'>Left</span> <span class='hs-layout'>(</span><span class='hs-varid'>ex1</span> <span class='hs-varop'>`mappend`</span> <span class='hs-varid'>ex2</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <a name="line-140"></a> <a name="line-141"></a><span class='hs-comment'>-- liftings of other arrow classes</span> <a name="line-142"></a> <a name="line-143"></a><span class='hs-comment'>-- specializations of general promotions</span> <a name="line-144"></a> <a name="line-145"></a><a name="instance%20ArrowReader%20r%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</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'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <a name="line-146"></a> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>ArrowReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-147"></a> <span class='hs-varid'>readState</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>readState</span> <a name="line-148"></a> <span class='hs-varid'>newReader</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>newReader</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <a name="line-149"></a> <a name="line-150"></a><a name="instance%20ArrowState%20s%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</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'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <a name="line-151"></a> <span class='hs-conid'>ArrowState</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-152"></a> <span class='hs-varid'>fetch</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>fetch</span> <a name="line-153"></a> <span class='hs-varid'>store</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>store</span> <a name="line-154"></a> <a name="line-155"></a><a name="instance%20ArrowWriter%20w%20(ErrorArrow%20ex%20a)"></a><span class='hs-keyword'>instance</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'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <a name="line-156"></a> <span class='hs-conid'>ArrowWriter</span> <span class='hs-varid'>w</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-157"></a> <span class='hs-varid'>write</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>lift</span> <span class='hs-varid'>write</span> <a name="line-158"></a> <span class='hs-varid'>newWriter</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>newWriter</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>rstrength</span><span class='hs-layout'>)</span> <a name="line-159"></a> <a name="line-160"></a><span class='hs-comment'>-- promotions</span> <a name="line-161"></a> <a name="line-162"></a><a name="instance%20ArrowAddReader%20r%20(ErrorArrow%20ex%20a)%20(ErrorArrow%20ex%20a')"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</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-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <a name="line-163"></a> <span class='hs-conid'>ArrowAddReader</span> <span class='hs-varid'>r</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-164"></a> <span class='hs-varid'>liftReader</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>liftReader</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <a name="line-165"></a> <span class='hs-varid'>elimReader</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>elimReader</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <a name="line-166"></a> <a name="line-167"></a><a name="instance%20ArrowAddState%20s%20(ErrorArrow%20ex%20a)%20(ErrorArrow%20ex%20a')"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</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-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <a name="line-168"></a> <span class='hs-conid'>ArrowAddState</span> <span class='hs-varid'>s</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-169"></a> <span class='hs-varid'>liftState</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>liftState</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <a name="line-170"></a> <span class='hs-varid'>elimState</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>elimState</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>rstrength</span><span class='hs-layout'>)</span> <a name="line-171"></a> <a name="line-172"></a><a name="instance%20ArrowAddWriter%20w%20(ErrorArrow%20ex%20a)%20(ErrorArrow%20ex%20a')"></a><span class='hs-keyword'>instance</span> <span class='hs-layout'>(</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-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a</span><span class='hs-layout'>,</span> <span class='hs-conid'>ArrowChoice</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=></span> <a name="line-173"></a> <span class='hs-conid'>ArrowAddWriter</span> <span class='hs-varid'>w</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>ex</span> <span class='hs-varid'>a'</span><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-174"></a> <span class='hs-varid'>liftWriter</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>liftWriter</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <a name="line-175"></a> <span class='hs-varid'>elimWriter</span> <span class='hs-layout'>(</span><span class='hs-conid'>ErrorArrow</span> <span class='hs-varid'>f</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>ErrorArrow</span> <span class='hs-layout'>(</span><span class='hs-varid'>elimWriter</span> <span class='hs-varid'>f</span> <span class='hs-varop'>>>></span> <span class='hs-varid'>arr</span> <span class='hs-varid'>rstrength</span><span class='hs-layout'>)</span> </pre></body> </html>