<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
p.MsoListParagraph, li.MsoListParagraph, div.MsoListParagraph
{mso-style-priority:34;
margin-top:0in;
margin-right:0in;
margin-bottom:0in;
margin-left:.5in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Calibri",sans-serif;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="#0563C1" vlink="#954F72">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt">Hello,<br>
<br>
The current version of Data.Bits is non-algebraic, in so far as the Bits class has<br>
1. a superclass constraint on `Eq`<br>
2. operations `testBit` and `isSigned` which return `Bool`.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">This is quite annoying, as myriad potential uses of the Bits class cover types for which these concrete observations are not possible. It leads to comments like the following in SBV:<br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-- | This instance is only defined so that we can define an instance for<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-- 'Data.Bits.Bits'. '==' and '/=' simply throw an error. Use<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-- 'Data.SBV.EqSymbolic' instead.<br>
<br>
We had this same issue for `Num` for years, until it eventually got fixed. And it would be nice to fix the situation for `Bits` as well.<br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">There are other aspects of the Bits API which are pretty clunky, but this is the one that is often a show stopper.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><br>
Philip<o:p></o:p></span></p>
</div>
</body>
</html>