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<p class="MsoNormal"><span style="font-size:12.0pt">Richard<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">I have just spent an hour plumbing the torrid swamp of binder visibility. There is bad naming confusion.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">We have<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo1"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">Visible<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo1"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">Specified<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l2 level1 lfo1"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">Invisible<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">The function isVisible returns True for Visible and False otherwise. But isInvisible returns True for Invisible
<b>and Specified</b>. And partitionInvisibles, filterOutInvisibleTyVars, filterOutInvisibleTypes etc all treat Invisible and Specified the same. That is, it’s really filterOutInvisibleOrSpecifiedTypes which is terribly clumsy.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Sometimes we need to pick up just the Inivisble args, and we don’t have a predicate for that (since isInvisible is taken), so you’ll see in Inst.top_instantiate we are reduced to saying (binderVisibility bndr
== Invisible).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">It’s all very smelly. The trouble is that
<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">In displayed types like (T a b), we display args that are Visible, but not Specified or Invisible<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">In visible type application like (f @t1 @t2) we can specify type args that are Visible or Specified but not Invisible.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Urgh. The trouble is that “invisible” is not the negation of “visible”, which leads to all kinds of confusion.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">I wonder about changing to<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l1 level1 lfo3"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">Explicit<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l1 level1 lfo3"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">Specified<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l1 level1 lfo3"><![if !supportLists]><span style="font-size:12.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:12.0pt">Implicit<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Then for display we display Explicit args only; for VTA we can specify Explicit or Specified args.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">So “not Explicit” doesn’t sound structurally like “Implicit” in the way that “not Visible” does sound like “Invisible”.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Simon<o:p></o:p></span></p>
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