<div dir="ltr"><span id="docs-internal-guid-01346169-8dcc-a9cf-7fed-432f7aa17a5a"><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:Arial;color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">I just watched Kenneth’s map talk from the EUC (<a href="http://vimeo.com/99747090">http://vimeo.com/99747090</a>).  He asked for feedback on maps, so here’s mine:</span></p>
<br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:Arial;color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">1. I ported a few functions from the lists module. Â The ones I found useful were filter() and mapfold(). Â I also found with() useful, which does the opposite of maps:without(). Â I would be very happy to see these 3 functions in the maps module.</span></p>
<br><br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:Arial;color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">2. In the talk there was a question about matching an empty map, and also a question about precise matching like how one would match a list.  I have always wondered similar things, so it got me thinking…</span></p>
<br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:Arial;color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">What if we use a "cons" in a map pattern to allow matching all remaining keys that were not selected in the main part of the pattern? Â This would be roughly symmetric to what you can do with lists and binaries. Â For example:</span></p>
<br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">#{ a:=A, c:=C | Rest } = #{a=>1, b=>2, c=>3, d=>4}. Â Â % Rest = #{b=>2, d=>4}</span></p>
<div><span><br></span></div><br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:Arial;color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">That in itself I think has limited use, but it could be used to exactly match a map (ie, no extra pairs other than those specified in the match):</span></p>
<br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">f(#{ a:=A, c:=C | Rest })</span></p>
<p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent"> Â Â when maps:size(Rest)==0 -></span></p>
<p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">…</span></p>
<div><span><br></span></div><br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:Arial;color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">If the pattern to the right of the bar is elided, we could take it to mean “match the empty mapâ€.  The previous example could be rewritten as:</span></p>
<br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">f(#{ a:=A, c:=C |}) -></span></p>
<p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">…</span></p>
<div><span><br></span></div><br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:Arial;color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">This also lets you match just the empty map as was asked in the talk:</span></p>
<br><p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">f(#{|}) -></span></p>
<p dir="ltr" style="line-height:1.15;margin-top:0pt;margin-bottom:0pt"><span style="font-size:15px;font-family:'Courier New';color:rgb(0,0,0);vertical-align:baseline;white-space:pre-wrap;background-color:transparent">…</span></p>
<div><span><br></span></div><div><span><br></span></div><div><span><br></span></div>Apologies if something like this has already been discussed.<br><br>Dan.</span></div>