<?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>src/Darcs/Witnesses/Eq.hs</title> <link type='text/css' rel='stylesheet' href='hscolour.css' /> </head> <body> <pre><a name="line-1"></a><span class='hs-cpp'>#</span><span class='hs-varid'>include</span> <span class='hs-str'>"gadts.h"</span> <a name="line-2"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Darcs</span><span class='hs-varop'>.</span><span class='hs-conid'>Witnesses</span><span class='hs-varop'>.</span><span class='hs-conid'>Eq</span> <span class='hs-layout'>(</span> <a name="line-3"></a> <span class='hs-conid'>EqCheck</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-conid'>MyEq</span><span class='hs-layout'>(</span><span class='hs-keyglyph'>..</span><span class='hs-layout'>)</span><span class='hs-layout'>,</span> <span class='hs-varid'>isIsEq</span> <a name="line-4"></a><span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-5"></a> <a name="line-6"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Darcs</span><span class='hs-varop'>.</span><span class='hs-conid'>Witnesses</span><span class='hs-varop'>.</span><span class='hs-conid'>Unsafe</span> <span class='hs-layout'>(</span> <span class='hs-varid'>unsafeCoerceP</span> <span class='hs-layout'>)</span> <a name="line-7"></a> <a name="line-8"></a><a name="EqCheck"></a><span class='hs-comment'>-- |'EqCheck' is used to pass around evidence (or lack thereof) of</span> <a name="line-9"></a><a name="EqCheck"></a><span class='hs-comment'>-- two witness types being equal.</span> <a name="line-10"></a><a name="EqCheck"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</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-keyword'>where</span> <a name="line-11"></a> <span class='hs-conid'>IsEq</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <a name="line-12"></a> <span class='hs-conid'>NotEq</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <a name="line-13"></a> <a name="line-14"></a><a name="instance%20Eq%20(EqCheck%20C(a%20b))"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Eq</span> <span class='hs-layout'>(</span><span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</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-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-15"></a> <span class='hs-conid'>IsEq</span> <span class='hs-varop'>==</span> <span class='hs-conid'>IsEq</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>True</span> <a name="line-16"></a> <span class='hs-conid'>NotEq</span> <span class='hs-varop'>==</span> <span class='hs-conid'>NotEq</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>True</span> <a name="line-17"></a> <span class='hs-keyword'>_</span> <span class='hs-varop'>==</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>False</span> <a name="line-18"></a> <a name="line-19"></a><a name="instance%20Show%20(EqCheck%20C(a%20b))"></a><span class='hs-keyword'>instance</span> <span class='hs-conid'>Show</span> <span class='hs-layout'>(</span><span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</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-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-20"></a> <span class='hs-varid'>show</span> <span class='hs-conid'>IsEq</span> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"IsEq"</span> <a name="line-21"></a> <span class='hs-varid'>show</span> <span class='hs-conid'>NotEq</span> <span class='hs-keyglyph'>=</span> <span class='hs-str'>"NotEq"</span> <a name="line-22"></a> <a name="line-23"></a><a name="MyEq"></a><span class='hs-comment'>-- |An witness aware equality class.</span> <a name="line-24"></a><a name="MyEq"></a><span class='hs-comment'>-- A minimal definition defines any one of 'unsafeCompare', '=\/=' and '=/\='.</span> <a name="line-25"></a><a name="MyEq"></a><span class='hs-keyword'>class</span> <span class='hs-conid'>MyEq</span> <span class='hs-varid'>p</span> <span class='hs-keyword'>where</span> <a name="line-26"></a> <span class='hs-comment'>-- |It is unsafe to define a class instance via this method, because</span> <a name="line-27"></a> <span class='hs-comment'>-- if it returns True then the default implementations of '=\/=' and '=/\='</span> <a name="line-28"></a> <span class='hs-comment'>-- will coerce the equality of two witnesses.</span> <a name="line-29"></a> <span class='hs-comment'>--</span> <a name="line-30"></a> <span class='hs-comment'>-- Calling this method is safe, although '=\/=' or '=/\=' would be better</span> <a name="line-31"></a> <span class='hs-comment'>-- choices as it is not usually meaningul to compare two patches that</span> <a name="line-32"></a> <span class='hs-comment'>-- don't share either a starting or an ending context</span> <a name="line-33"></a> <span class='hs-varid'>unsafeCompare</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>p</span> <span class='hs-conid'>C</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-keyglyph'>-></span> <span class='hs-varid'>p</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>c</span> <span class='hs-varid'>d</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Bool</span> <a name="line-34"></a> <span class='hs-varid'>unsafeCompare</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>IsEq</span> <span class='hs-varop'>==</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varop'>=/\=</span> <span class='hs-varid'>unsafeCoerceP</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <a name="line-35"></a> <a name="line-36"></a> <span class='hs-comment'>-- |Compare two things with the same starting witness. If the things</span> <a name="line-37"></a> <span class='hs-comment'>-- compare equal, evidence of the ending witnesses being equal will</span> <a name="line-38"></a> <span class='hs-comment'>-- be returned.</span> <a name="line-39"></a> <span class='hs-layout'>(</span><span class='hs-varop'>=\/=</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>p</span> <span class='hs-conid'>C</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-keyglyph'>-></span> <span class='hs-varid'>p</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>b</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <a name="line-40"></a> <span class='hs-varid'>a</span> <span class='hs-varop'>=\/=</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>unsafeCompare</span> <span class='hs-varid'>a</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>unsafeCoerceP</span> <span class='hs-conid'>IsEq</span> <a name="line-41"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>NotEq</span> <a name="line-42"></a> <a name="line-43"></a> <span class='hs-comment'>-- |Compare two things with the same ending witness. If the things</span> <a name="line-44"></a> <span class='hs-comment'>-- compare equal, evidence of the starting witnesses being equal will</span> <a name="line-45"></a> <span class='hs-comment'>-- be returned.</span> <a name="line-46"></a> <span class='hs-layout'>(</span><span class='hs-varop'>=/\=</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>::</span> <span class='hs-varid'>p</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>p</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>b</span> <span class='hs-varid'>c</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</span><span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <a name="line-47"></a> <span class='hs-varid'>a</span> <span class='hs-varop'>=/\=</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>IsEq</span> <span class='hs-varop'>==</span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-varop'>=\/=</span> <span class='hs-varid'>unsafeCoerceP</span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>unsafeCoerceP</span> <span class='hs-conid'>IsEq</span> <a name="line-48"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>NotEq</span> <a name="line-49"></a> <a name="line-50"></a><span class='hs-keyword'>infix</span> <span class='hs-num'>4</span> <span class='hs-varop'>=\/=</span><span class='hs-layout'>,</span> <span class='hs-varop'>=/\=</span> <a name="line-51"></a> <a name="line-52"></a><a name="isIsEq"></a><span class='hs-definition'>isIsEq</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>EqCheck</span> <span class='hs-conid'>C</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-keyglyph'>-></span> <span class='hs-conid'>Bool</span> <a name="line-53"></a><span class='hs-definition'>isIsEq</span> <span class='hs-conid'>IsEq</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>True</span> <a name="line-54"></a><span class='hs-definition'>isIsEq</span> <span class='hs-conid'>NotEq</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>False</span> </pre></body> </html>
