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<p class="MsoNormal"><span style="color:#1F497D">(I sent this to ‘libraries’ but Kim-Ee suggested adding Café, where so many smart people hang out.)</span><span lang="EN-US" style="mso-fareast-language:EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif"">Friends<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif"">Some of you will know that I’ve promised to give a talk about
<a href="http://hackage.haskell.org/package/lens">Edward’s lens library</a> at the
<a href="http://skillsmatter.com/event/scala/haskell-exchange">Haskell Exchange</a> in London next Wednesday (9<sup>th</sup>). I did this to give everyone (including me) a break from GHC hackery, and also to force me to learn about this lens voodoo that everyone
is twittering about. Edward generously gave me quite a bit of one-to-one attention last week (my hair is still standing on end), but this message is to ask your help too.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><br>
<b>Specifically, I’d like to give some compelling use-cases</b>. If you are using the lens library yourself, could you spare a few minutes to tell me how you are using it? I expect to cover Lens and Traversal but not Prism.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif"">The use-case everyone starts with is nested records, but I’d like to go beyond that. The next levels seem to be:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">ˇ<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-family:"Verdana","sans-serif"">Lenses as views of data that isn’t “really there” e.g. regarding a record with rectangular coordinates as having polar coordinates too.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">ˇ<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-family:"Verdana","sans-serif"">Lenses and Traversals that focus on elements of finite maps (Control.Lens.At)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif"">What else? I’m sure you are using them in all sorts of cool ways that I would never think of, and I’d love to know.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif"">Please don’t tell me anything secret! To give everyone the benefit I may just concatenate all the replies and send to you all, so please say if you don’t want me to do that with yours.<span style="color:#1F497D">
</span><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif"">And don’t burn too many cycles on this...I don’t want to waste your time, and I can always get back to you if I can’t understand what you say. Sooner is better than later...Weds is coming.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif"">Simon “Edward’s prophet” PJ<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Verdana","sans-serif""><o:p> </o:p></span></p>
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