On Mon, Sep 20, 2010 at 12:47 PM, Simon Peyton-Jones <span dir="ltr">&lt;<a href="mailto:simonpj@microsoft.com">simonpj@microsoft.com</a>&gt;</span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">







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<p class="MsoNormal"><span class="Apple-style-span" style="font-size: 15px; color: rgb(255, 0, 0); ">Thomas had it right; it’s just a particular kind of fold.  The key parts of the traversal would be:</span></p></div><div>


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<p><span style="font-size:11.0pt;font-family:Symbol;color:red"><span>·<span style="font:7.0pt &quot;Times New Roman&quot;">       
</span></span></span><span style="font-size:11.0pt;color:red">Occurrences.    getExpr g (HsVar v) = g_occ g v</span></p></div></div></div></div></div></blockquote><div><br></div><div>Don&#39;t I need to work on LHsExpr rather than HsExpr? How would I otherwise get the location? </div>

<div><br></div><div><div>    getExpr :: Gather v res -&gt; LHsExpr v -&gt; res</div><div>    getExpr g (L loc e) = case e of</div><div>        HsVar v -&gt; g_occ g (L loc v)</div><div>        HsApp e1 e2 -&gt; g_union g (getExpr g e1) (getExpr g e2)</div>

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<p><span style="font-size:11.0pt;font-family:Symbol;color:red"><span>·<span style="font:7.0pt &quot;Times New Roman&quot;">       
</span></span></span><span style="font-size:11.0pt;color:red">Binding&gt;          getExpr (Lam v e) = g_del v (getExpr g e)</span></p></div></div></div></div></div></blockquote><div><br></div><div>I still don&#39;t quite the purpose of this, is it to say the v is now shadowing whatever had the same name in the scope surrounding the lambda? Or is &quot;g_del&quot; intended to mean &quot;g_declaration&quot; and capture the declaration sites (and if so, how I know if it&#39;s a exported top-level declaration or not)?</div>

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<p class="MsoNormal"><span style="font-size:11.0pt;color:red">Does that help?  Maybe one could generalise a bit. </span></p></div></div></div></div></div></blockquote><div><br></div><div>Definitely. Thanks for the pointers.</div>

<div><br></div><div>Cheers,</div><div>Johan</div><div> </div></div>